Right. If the amount you owe the lender or lenders is more than the current market value of your home, then you are "short". But you DO NOT have to be delinquent to have the lender agree to a sort sale. Your "hardship" situation is important, though. Anyway, it looks like you are in good shape, I am assuming. Thatis, you do have equity in your home and will nto be short, right? If you are, make sure your listing agent is distressed property certified.
The best way? Talk to a professional realtor in your area and ask her/him. Typically, market value is defined by comps and the best source for data on comps is the local MLS. In the end, market value is determined by what buyers are willing to pay and how much they are willing to pay is driven by most recent sales.