Boats are a bit different. The normal thing is to have an accepted offer subject to satisfactory sea trial and survey in place before anything really happens (certainly at a brokerage this would be the case). Private sales are another thing and they may go differently, but as a seller I'd still want to see some good faith money before taking someone out for a sail (mainly to avoid fender-kicking looky-loos that just want a free sail)
This is one area where a broker smooths thing..they provide at the least a neutral place to hold the deposit while the deal progresses, and can facilitate renegotiations without things getting personal.
As for a survey.... It's still recommended unless you feel you wouldn't be bothered to throw away $5k. The $400-600 involved is almost always recovered in a renegotiated price for the problems found. Should you end up with a boat with major problems, not only might you essentially be "out" your initial investment, getting rid of such a boat is difficult and might cost you more. (Worst case scenario, of course). If it turns out that the boat is pristine and has no issues, then you've got a lot of peace of mind for the future.
If your seller is willing to proceed on an agreement for sale contract and you get a good vibe from him, carry on with eyes wide open. Try for a minimal deposit in case things go seriously south and recovery becomes an issue.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)