If I'm having a difficult time finding comps I will go to registry of deeds and search out private sales.  I may even have to adjust my radius.  Happens to me when I'm working on a commercial property, mixed use or multifamily.

We use Cloud CMA that is provided by our mls.

Not everything is in the MLS. Counties around here have full time assessors, and they are actually pretty accurate with their assessed values, so I look at those also. Our county also provides a list of " Neighborhood Sales" that weren't in the MLS. I look at all the information I can find.

I use all sources and the platforms, as I explain to my clients that some buyers will be using those to determine their valuation for an offer price.

Yes, cross check with all available sources and County records must be included but MLS is gonna be the first stop  . . . title company records are accessible and helpful too. They're also accurate as County can take 6-8 weeks to update recordations and title companies have it much sooner.

I did utilize the MLS, go through the county records for FSBO and also, assessor records.  Only if I could not find comps or needed a new and accurate measurement did I enlist an appraiser.

Non MLS sales can be low in selling price, especially if they are a private family to family member sale. A home that is sold on the "open market" is the best comp.

Depends upon the property. 

 The MLS will usually suffice for a cookie-cutter house in a subdivision with a lot of recent or current sales activity.

If the MLS comes up dry, a search of Public Records might show FSBO's or other properties that didn't involve a  Listing Office.

 A truly unique property, such as a historic home, a house on acreage, or a house with a large stretch of waterfront, I may have to call an Appraiser for help.

 And - I won't use Zillow or Realtor dot com or Redfin to create a CMA, but I will look at those sites, because chances are that my Seller (and potential Buyers) has or will preview those websites; I need to be ready when they say, "But Zillow says..."

Use all sources available.

Peter...

Until I am satisfied, all sources consulted Peter Mohylsky, Broker good one

I use all available resources.  

I do quite a bit of research, so definitely all sources. A while ago, I had to do a retrospective CMA for probate and it involved describing the economic/real estate environment of several years ago, corresponding to the time of death of the property owner.  MLS would not be able to offer that kind of information, but was helpful with the then-current home prices. 

Depends on the property.  If there are plenty of comps in the MLS then I use that.  If it's unique then  I use multiple other courses, like public records and even have a great relationship with several appraisers I can call.

I use all resources available to me when preparing a CMA.  My starting point is always the MLS and Public Records. Once I have completed the market analysis, I pull up the Zillow, Redfin and Realtor and have them available in my back pocket in case the conversation comes up.  

I recently started using RPR and the use of ai and in extreme difficult cases I have reached out to my favorite appraiser in town.

MS, RPR and ai

Since we don't have an MLS, my first source is Streeteasy (built exclusively for NYC, bought by Zillow) and if the comps are not captured there I go to my broker site, then NYC Dept of Finance.

We recommend RPR, but we are looking at other sources to produce a great CMA.  What our MLS produces is not all that great.

Always use all available resources we have, including private sales. There are many communities in my area that sell privately. It's mind-boggling because if I were a seller in those communities, I would totally go with MLS...and make more $$$$$! Private sellers make me just shake my head!

I only used the MLS Peter Mohylsky, Broker unless it was a rural property outside of the City. Those were often very difficult.

I usually check everything available to me. 

When active I used all sources available. With unique properties I suggested the seller get an appraisal and make it available for review with potential buyers. Luckily I did not need appraisals often. 

That's one of those "it depends" questions.  In a "cookie cutter neighborhood" or on the lake the MLS always provides enough comps for an easy place to gather data for the CMA.  The exception is generally a log cabin on the lake because we only have a handful of those.  Off water properties on acreage generally takes a bit more research into public records.  Our state system we look up properties on has a great "see recent sales" button that is super helpful and we can "see nearby sales" as well.  I also have a great working relationship with several local appraisers when I am doing a CMA on a unicorn.

Peter Mohylsky, Broker if the property is within my market area, I have an idea as to what it will sell for or should be listed at. I do use the MLS to review current comps. 

Depends on how robust the MLS is on it's own. 
For rental comps I use 4-8 sources, hardly anything from MLS, but for equity, the MLS typically offers enough in most areas of San Diego.

MLS, conditions, orientation, location and local knowledge.