Doyle, 

You have received some excellent advice. I say do them in this order.

Eliminate source of odor.

If it is gone then (as a few have mentioned) run an Ozone machine for a day or so. Just don't stay in the house while it is running as it can irritate lungs and mucous membranes. Then the fresh paint and I might add that adding a bit of Vanilla extract in the paint can (stirred in) can help. 

I have an ozone machine and they work well. (we run into odors all the time when listing whether it is pets, smoking or other odors) 

An ultra-violet (UV) light (black light) can be used to reveal stains on carpets and walls that are not visible in normal light.  Cleaning carpets won't help if the odor is in the carpet padding.

Bury the dead bodies in the back yard of a competitor.  Then make an anonymous call to the police.

I am going to suggest an ionizer machine.   You can rent them.  Store some activated charcoal in a nice container with holes that no one will notice.  Baking soda all over carpeting and upholstery and vacuum it after it has been there for about four hours.  But there are other great suggestions here, too!

@Debra Peters, I was thinking the same thing..1 tiny dead mouse smells a long way.

Ozone machines do help.  But you have to find the source and remove it....blehhh.

Good luck with your open house.

It depends. Why it smells that bad?

If the property is wet and has mold, little you can do, open house might be a bad idea as well. If the owners have pets who created that stink,  a cleaning company can help, but not for long, the stink will be back.

Have the bodies removed!  Just kiddng.  Carpeting and drapes, as well as fabric in furnature absorb odors. That is the first things I would address.

baking soda on the carpet absorbs a lot of odor, so does cat liter and an open bag of BBQ briquettes (unsued ones...).

Find the cause of the odor and deal with it!  Fresh paint can help, so can incense, sage, etc.

First, identfy the source of the smell. Running a dehumidifier could help some. Get a couple cans of Febreze. The original, not any of the scented ones. Placing some boxes of baking soda around might help a little as well.

I would contact a cleaning or restoration company.  Do you know if the smell is coming from the floors/carpets, basement or all over?  Maybe an animal died in the basement, crawl space or under a porch.  Dead animals give off a rancid smell.  I tiny dead mouse also leaves a nasty stench!

Doyle,

I would hire a cleaning company that cleans everything, walls, ceilings, cupboards, every nook and cranny.  I am sure there is someone who does that in your area.  A

Find the source get rid of it. Call a pro if you can. It all depends on what the odor is. Had a couple who was going to list. They decided to tear out the carpet an clean the floors by the pros, put in new carpet and padding, painted the walls. Had it professionally clean. I put a CMA together and they chose not to sell:(  That was  4 years ago and they're still there. Oh, well! They did give me a couple referrals (2 sells within 4 months and we closed. So I still didn't lose.

Doyle,

You use an Accredited Staging Professional (ASP) to do your "dirty work" and to communicate the difficult information. We're your "bad guy"!! I do all of this when I meet with the Homeowner that the Broker has introduced me to BEFORE any showings, MLS pictures, Open Houses, etc. as the Broker's ASP stager.  You get a devoted ASP stager in your area and your issues would be resolved -- NO MORE listings with "dead people" smells!!  I have a very sensitive 'smeller' and I tell the Homeowner firmly, but politely, that "this" has got to be resolved before buyers will be attracted to "your lovely abode".

Just reading the comment string makes me thing back to the time my buyer had the seller remove the bat guano from the attic...30 garbage bags weighing about 30 lbs each....

Could be animals that have died in the crawl or attic. I would have it well cleaned, carpet shampooed with an ordor remover(smells like bubble gum for 2 weeks - ordor gone) and rent and ozone machine for a few days. Those are really great!

As Jill Moog just mentioned, remove the source.  Then after the house is cleaned I have sprinkled half a box of baking soda onto the carpet in each room.  Leave it over night then vacuum.  (don't forget to empty the vacuum right away) After you vacuum then I put 1/4 cup of white vinegar into a small cup and placed it in or beside the floor vent.  The next morning the house smelled fine.  I have used this on 3 houses and it has worked every time.

I had a listing one time that was so bad it made everyone gag, it was a bank owned and they were not willing to put anything into clean up.  It was heavy dog, cat, garbage and smoke.  Keeping up with your subject line....  After trying all the usual things I wound up getting a special cleaner from the mortuary.  It did a great job and might be worth a try.

First, find and remove the cause of the smell. If there are spots/stains causing the odor you can try using a natural enzyme formula like "Natures Miracle" or "Kids and Pets", it really works great!  You may need to  remove the entire carpet/padding if the smell has seeped through but use the enzyme formula on the subfloor as this is eliminate the smell from coming back. Then clean the rest of the house and  a fresh coat of paint should do the trick.

Paint, Fabreeze, Carpet Cleaning, and check the attic for dead rodents.

Dana - Wow I had never thought of adding vanilla extract to paint.  I have a couple of rental apartments and that is an excellent idea!

That ionizer idea may work. I don't kow what dead people smell like.

We've used some ozone treatments in the past that might help then some fresh paint afterwards can seal the deal so to speak. There are times when we never made it past the front doors also.

Some odors just can't be removed easily.

I had a small ozone/ionizer machine I used for a while.  That help a lot

Good answer here.

Other than dealing with the source in general painting is the best way to get a nice new smell in the place.

Wow these are some good suggestions! I wonder though, could there be a negative outcome if you just cover up the smell, and not address where the smell is coming from?

Loving all these tips for getting bad smells out.

May I recommend clothes pins for the nose along with foot booties by the front door.   :-)   

I read all the posts as I needed this knowledge as well.  Thank you

Is the house vacant or occupied? Is the seller aware of the problem?  If it's truly a dead animal, perhaps a skilled exterminating company can locate and remove it?

If possible, have all of the soft surfaces such as carpets, window treatments, upholstered furniture, etc.  removed.  Also,  when an owner has lived in a house for a long time, the closets can develop an "old" odor. This is just an accumulation of years worth of various odors that have collected on the clothing. Short of moving everything to storage, tucking unwrapped bars of soap in the closets helps freshen the air a bit.  The dryer sheets and lemon peels help as well.

If the owner's not on board, your options are limited.  Good luck. 

I realize that we want to "hide" the smell to begin with, but as mentioned, if the source is not found, I hope the issue is addressed before someone buys it - hate for a lawsuit to pop up later.

All of the suggestions in the comments and post are great!  Ozone machines can work wonders. The suggestion of vinegar water simmering on the stove is new to me.

I had a house with a stong curry smell.  We cleaned and cleaned - learned that curry becomes an oil and coats everything in the house.  Underneath cabinets, behind the stove, refrigerator.  I always came to the open house early,  cooked white vinegar and water on the stove, febreezed like crazy and opened all the windows.  It was a little less obtrusive but...was still present. 

Hire or suggest the client hire a home stager to work with the client to turn this situation around and get the house in great shape for showing. Let the home stager deal with this situation so you can spend your valuable time selling homes rather than dealing with "where the bodies are buried":).

There have been some fine answers here.  I suspect you probably don't want to spend any more than  a few bucks to deal with the issue.  The quickest way to get you (at least) through showing the house is to get the plug-in air fresheners and scatter them, strategically, throughout the house.  Crack the windows to allow it to breathe and not be overpowered by the perfume.   I know this might sound a bit much but I always keep a bottle of neutrally-scented Febreeze in the car if I'm ever meeting someone at a house.  Unlike the others, Febreeze literally changes the air instead of adding perfumed odor to the existing smelly air.  Find and neutralize the source of the odor, to be certain, but the low-tech approach will probably get you through as long as there isn't something truly terrible causing the odor.

Oh I think it is very difficult to get odors out of a home..animal odor, strong cooking odor, mildewy smells--even cleaning carpet, curtains, etc doesn't help at times.  Dead people smell?  That's a new one for me!

thanks for all responses

Ozone machine.

Few very good suggestions for sure.

Doyle, well, you gotta get rid of the dead guys first!  Sounds like this one is way beyond a little vanilla on the light bulbs.  A couple of weeks ago at an office meeting we shared some fixes, and charcoal in bowls in the worst rooms was supposed to work.  Someone else suggested small bowls of vinegar placed in less than obvious places.  Good luck with this one!

You didn't say if the house was vacant or not...

assuming a vacant house, use those plug in or counter top air fresheners for several days before the open. The day of the open, spray with Febreeze and open some windows.

If the house is occupied, just ask them to open the windows the morning of the open and ask them to vacate an hour or so before. Get there early, wipe off dirty counters or whatever is contributing to the smell. Light tea light candles in kitchen and bath, and spray Febreeze on all the furniture and carpets and drapes.

Febreeze is the best for stinky listings.

Hire a professional cleaner.

I haven't read all the comments.  Has anyone else suggested marketing the home to Zombies instead of freshening up the smell?

Alternatively, citrus and herbal odors are best for conveying a clean, fresh smell. Squeeze lemon peels to release the citric acid in every room.

Strong odors of any type divert attention from the house for sale.

Curry and cigarette smoke have been problems with buyers with me.

Animal urine can get into flooring and below.  It's not the urine that causes the odor, it's the bacteria that grows in it. 

If we smell it in a house, we just cross that house off.