I'd amend Dave's advice above as follows -
Make your own inspection before making an offer - I wouldn't accept a broker's word on anything. If the broker won't let you inspect the boat without an offer, keep walking.
If you don't find anything horrifying during your own inspection, you make an offer, and usually a deposit, then you get your sea trial, etc as described above.
I would also really emphasize what Dave mentions about amending your offer based on sea-trial/survey results, but I'd suggest that you hold it all in for after the survey unless you find anything really flagrent.
Try to find out how long the broker has had the boat, this can be a good clue to how motivated the seller is - my boat had been sitting at the brokerage for over a year - and come down very significantly from the initial asking price already.
Also, don't take the broker's advice on surveyors, and ask around - find the most particular person you can to help you identify every single problem with the thing, then itemize those to the broker as reasons why you won't pay more than _____ for the boat.
Best of luck,
Sailing a '74 Challenger 40' Ketch rig out of San Francisco