Questions about boat buying process...
As others have remarked you generally look at a number of boats before you find one that meets your needs and expectations and is then worth making an offer & having a survey. In your case it would be typical for you to go look at the boat, if it passes your inspection & you want it, you could then make an offer "contingent" on survey to your satisfaction. If there are issues noted on the survey you renegotiate the offer to reflect. Usually you go for a price reduction or the seller to pay cost of needed repairs.
A surveyor will generally only go so far as to say something like "I see no reason for you to not buy this boat" or " This boat should definitely have such & such done right away."
If something is found on the survey that sours the deal for you it will cost you for the short term haul-out ($150 - 200) and survey $10-$12/ foot, around $400 total. Much better then paying $20,000 for boat and then discovering it needs a $5,000 engine.
I see Jeff has already given you a more detailed answer before I could post this, his idea of using a surveyor for a "quick look" is a good one if you can''t make that first look yourself, they all look and sound good in the ads. Usually the first time you see the boat you will know if it is worth a closer exam or just walk away. As he mentioned if it seems to be "the boat" you look in every nook and cranny, you will either like or dislike what you see in areas normally hidden & may find things you want your surveyor to REALLY check for you. Also researching the boat you may find areas of concern with that particular model the surveyor may be unaware of.