The original loan amount has no bearing on the sale. The bank is interested in two things, 1) the offer, 2) fair market value. If you nail it on the head, and you're the only one in the running, and the listing agent only submits one offer to the lender, then you're probably going to get it.
Your real estate agent should be savvy enough to work with the listing agent to determine if it's even worth your agent's and your time to bother with it. If the listing agent hasn't priced it right, and your agent doesn't know what market value should be, then you'll miss the mark and it will result in a counter offer from the bank.
The goal of the listing agent is to advise his/her client to accept a contract that everyone agrees will make it through the bank on the first try.