Let's take the myth and mystery out of short sales. Questions like this are a good indicator of why so many bitterly disappointed buyers post tales of woe and suspected misdeeds in this forum.
A short sale is the least undesirable of two undesirable alternatives. Lenders offer short sales in an effort to minimize their losses. Properties sold on a short sale are usually in better condition than foreclosed properties. Many people deliberately vandalize homes they lose to foreclosure, while people who sell short are generally more responsible. Hence, the properties are generally more marketable, even if they have not been vandalized.
Lenders generally accept list prices at the low end of the FMV in hopes of making as quick a sale as possible, but the list price is the FMV. As offers come in, lenders sit on them for a protracted period of time--shopping for the best offer, and the highest offer will prevail. This works for them, because many buyers make full price offers, knowing that they are a bargain. When they really want a given home, some buyers even up the anti a tad in the belief that they need to do so in order to get the contract. They do, and many buyers who low-balled under the belief that the lender is desperate do not. The exceptions are likely for those properties that are in sub standard condition. The bulk of the sales that close are likely those that are right at or only a few percentage points below the asking price.
Some low-ball offers do make it, but I doubt that the stats are readily available or worth the effort to research in order to determine how significant a portion of sales are low-ball offers. A good agent is going to understand the market dynamic and advise their client accordingly, and all good agents know that the clients of other good agents are getting this advice.
None of this is to say that agents do not need to do a CMA for a client who is interested in a short sale property. It absolutely should be done in order to satisfy both the agent and buyer that, yes, the property is a bargain at the price for which it is being offered.
Lenders use strategic criteria in short sales, not formulaic criteria. In a market where values have declined by 25%, were a lender to take an offer of 85% of the FMV, they would be taking an ~40% hit on their investment (remember, they are also absorbing seller settlement costs). Moreover, as explained above, they do not need to take such a hard hit.