The price of a house will depend if it is a buyers market or a sellers market (these change all the time).
A few years ago, when we had the financial crash, it was a buyers market as people were reluctant to take out a mortgage, also banks tightened up on how much they would lend.
During that time you could offer less than the asking price as there were few other buyers around.
But at other times, if the financial market is strong and banks will lend decent mortgages, and there are lots of buyers and not many sellers, then it is a sellers market and you will probably have to offer over the asking price to get it (or may even be gazumped).
So you need to decide (in your area) if it is a buyers market or sellers market.
If you are not sure just offer a figure, they can only say no, then keep raising it till they say yes.
No point it paying more than you need to.