judging value in a beat up market

[Rob Franks]

with the real estate market in its current decline i have been noticing that almost every house for sale is advertised at below apprasial value. how do can you judge if this really is a good deal. I cant really find a formula or anything that says how much below appraisial value makes it a good deal. it was a lot easier to assess value in a good market, because it seemed like anything below appraisal was worth the investment. however now that the supply out weighs the demand in most areas. i have no idea how to correctly judge value. anyone have any tips, or theories? thanks.