It's just called due diligence. you should know what you can afford and the costs of whats going to go with it. thats why at the Wynn in Vegas they charge 10 bucks to come in and look at the ferarris, buy one and you dont pay it.
When looking you should have your ducks in a line so you dont look like a tool when the time comes. As I said in another thread, if you are worried about having to redo the motors in a few months and cant afford it, then you probably cant afford the boat to begin with. buying the boat is the easy part, making sure you have the insurance, tow vehicle, trailer are just as important.
When I bought the Tiger, I already knew that it was with no trailer, I called Myco got the price, and talked with a loan guy, when he dropped the ball at the 11th hour. Another broker picked it up and gave me verbal approval in 30 minutes, had the paperwork done in a week. It was because I knew what i wanted to spend, had the down payment and knew all the expenses before Victor and I agreed. he gave me his best price and the deal was done. I actually made a payment and kept it at Victors marina for a month because Myco had a backlog. I had never met him until I picked it up and made a friend in the process.