If the seller wnats to sell the property he will deal with whoever has
the best offer.

Do your research. If there are several houses in an area that you would
consider then take the asking price of each seller and go with a low
bid on the best property.

If it is a hot market area there may be bids higher than the asking
price.

A poor area nad you could go 60% of asking price.

You can often find out how long a property has been on the market by
asking the agent for a property info sheet.