Sometimes but not usually.
The buy now price goes away when the first bid is entered. Sometimes people get into a bidding wars after the buy it know price disappears. Usually the seller will set the buy it now price high, but sometime they underestimate how popular an item will be.
Only if the bidders are daft. If you can be sure of getting it at a particular price by hitting the Buy It Now button, why bid more?
Why would someone bid higher than the Buy Now price when they could simply hit the Buy Now button and get it for that price ?????????
Some do, some don't. It depends on what the item is.