As has been said, it all depends on the comparable sales and what the value is in today's market.
Consider then the competitive market we are in, and offer accordingly. Even short sales are receiving mulitple offers very quickly.
But on a short sale be prepared that, even if you are not selected as the buyer submitted for the short sale approval, you may be contacted later if the first buyer walked. Have your agent keep in contact with the listing agent. By the time the seller's lender approves the sale, the first buyer might be gone, and the lender may have responded with what price would be acceptable.
That's all to say, make your best (educated) offer that you can, but if you're not accepted at first, don't give up on it until it's actually SOLD, or you've bought another property.