Lynn
It is well known that any property will sell at the right price. The sad fact is that in any given market there are 80% of the listings that are not marketed correctly, over-priced, and not prepared for sale.

A sharp Realtor will try to work only with clients that need to sell. That means that if they know that over-priced homes will not sell, when they figure out that your home will not sell, they need to invest their limited time working with a seller that has a home that will sell.

How much you owe, how much you paid, how much you need to net, do not matter to buyers. You might want to look at the stats for your area (see link). If the market is headed down, you do not want to be an agent with an overpriced listing.

If the sale of your home is requiring a price that will cause you to owe at the closing table, then maybe you shouldn't be selling.

I am not sure I exactly understand your question? Are you saying your Realtor wants out of the Listing Agreement if you don't agree to do a short sale?
If so; I would imagine that the Realtor strongly feels that the only way to sell your home is for that lower price. Most (good) Realtors, do not wish to waste time, money and energy marketing a property that won't sell for a certain price. I would get a 2nd opinion form another agent as to your homes value. But make sure the agent is showing you TRUE Comparable sales.
You should NEVER choose your Realtor simply by just what they claim they can sell your home for.