You can always bid lower, but there's always a chance you may be over-bidded.
In certain areas, home values are starting to stabilize and even go up. Homes are also getting into bidding wars and selling for over asking price.
So it's not guaranteed if you purchase a home today that it's value may decrease lower than your mortgage.
Hire a Realtor to best advise you in your desired area and discuss with you the trending sales activity and current market values. Doing so may help ease some of your concerns.
Best with purchasing a home!
You can submit a lower offer on a home whenever you want, however the seller is not obligated to sell you the home. If you want to give me a call I would be happy to answer all of your questions and address any concerns you have,
Coldwell Banker - Robert Michael Realty
(732) 239-7452 Cell