Just to clarify or emphasize what I mentioned below...
Market value is "the price at which the property would change hands between a willing buyer and a willing seller, neither being under any compulsion to buy or to sell and both having reasonable knowledge of relevant facts."
"Other examples of sales that would not meet the test of fair market value include a liquidation sale, deed in lieu of foreclosure, distressed sale, and similar types of transactions. There is no longer any such value in real estate appraising as Fair Market Value, the correct term is Market value" - wikipedia (also checked in my old real estate course book)
In lamens terms: Market value is set by the buyer. It is what the buyer is willing to pay for real estate or how much the buyer values the property. Because not every buyer values property the same, it is up to the individual person to determine.
Not all comparables should be used in a CMA. Recently sold homes that are comparable in size, features, bedrooms, etc. may be foreclosures/ distressed sales/ or short sales- make sure your agent isn't using these as comparables.
That being said- It is good to know what these properties have sold for as well, because you may be able to get a similar property for less by purchasing a bank owned or short sale property.
If you're worried about your offer...most people make their offers contigent upon financing, an acceptable home inspection, etc, and it can be pretty easy to back out under those contingencies. Usually, this is standard and written in the purchase agreement- most agents use pre-written agreements with these contingencies available to "check" with a time frame to allow for inspection...all making it easier for buyers to back out in case something is wrong. If you have problems backing out...you've got "lawyer issues."
Let us know what happens..what you find out...what the CMA tells you...