If your looking at buying a new boat use the search tool for this board. I went through this at the begining of the season and got tones of help from the guys on this board.
My advice: post the boat specks ie. length,width, make, year, motor hp and year and price aksed- Guys with a good idea of what the boat is realy worth will pipe in.
Take it to a marina for a good look over and compression test. If the current owner is not ok with that walk away.
This is a good start and im sure you will get the rest of your questions answered as they come up.