Why is this question asked anonymously?   

Always.

Whenever they don't feel right about their agent representing both sides in a transaction, which to me would be quite often.

When the agent cannot be trusted to uphold their fiduciary duties to both parties. 

Now.

Because it is IMPOSSIBLE to sell a home for the highest price for the seller and get the home at the lowest price for the buyer at the same time

When their agent uses an anonymous image.

always.

every time.

Eve

When they do not have a comfort level or a thorough understanding of dual agency is.

Every instance!

When they are more interested in a either a "win/lose" or a "no deal" rather than a "win/win".

I don't see many situations that it is even in the client's best interest.

Anytime!

I am against duals because it is a barbaric practice. Killing someone over a slight? Terrible!

I have seen the many answers against dual agency.  Not that I disagree with them, but there are times I've seen an advantage to the buyer to accept dual agency.  In a hot market, I believe buying through the listing agent can give the buyer a better chance of getting the home they want.  There are risks in this, if they are willing to accept them.  

I'll share two opposing concepts: I'd personally never do dual agency if I didn't have a relationship already with the agent. As a buyer or seller, I do not recommend it.

Now, conversely, as a Realtor, I do them quite often.

If you have an issue with dual agency, you really are saying you have an issue with the agent.

Dual agency was how we did real estate until the 1970's. I do it on a few deals every year. I pass on doing it occasionally, it's a gut feeling for me as an agent...I'll bring in my buyer's agent to rep the buyer and I remain arm's length with the seller, even though both sides ultimately are mine.

The answer is not the same in all of the states. Talk with your broker.

When they feel their best interests are not being represented. Personally, not a big fan of dual agency.

If they don't feel comfortable with the situation, they should say no. 

It is their decision. Probably if they do not trust their agent? 

If they don't like it, say it in the beginning - at the time of signing the contract.

When there is no trust!

It's up to the client. They should be informed and definitely understand the situation.  It's not always a good decision.

What Troy Erickson said!

When they don't want to allow it.

It is up to him.

If they need advice , counsel,strategy in the transaction !

When they expect, deserve and want to actually be REPRESENTED!

Colorado no longer has dual agency.

If they don't want their best and most vested salesman (the listing agent) to sell the buyers.  No buyers agent is going to do as good of a job selling the home as the listing agent can.  Plain and simple.  Why go into battle with your best weapons off the table?

What about a Transactional Agency?  Throw that at your instructor.

In Oklahoma we do not have dual agency.

IMHO always to Single Agent Dual Agency...

Always.  

in my opinion, ALWAYS..... everyone needs proper representation....pick a side and stay there....

Any time they want to...

When they are not completely comfortable with the agent in question as to their integrity. It can work and is legal in some states, but not in all.

If they don't agree to the terms of the dual agency disclosure.

Most of the time!

do the right thing

Stay away from what you do not understand.

This applies to agents and buyers and sellers.

When they are uncomfortable