If it is a more "standard" contract...you are able to walk any time after the survey, for any reason, if you do not like the results of the survey for what ever reason...
In the real world, since you now have some $$ in the game and likely want a boat, the broker counts on you to now negotiate those things in the survey that you feel are show stoppers. The seller nor he, are going to be real interested in negotiating B or C list stuff or nickle/dime stuff...They better negotiate the A list stuff, as much of it will prevent you getting insurance if it is not fixed.
If in fact there is a 5% clause in the purchase contract, then you need to read it and see what you have signed on to. I certainly would not look for a broker, no matter what the reputation or past experience has been, to look out for YOUR best interest....he is looking for a commission, nothing more.
I have always done the sea trial in conjunction with the survey, I notify the owner/broker that I want a cold engine, and potentially the boat for the whole day. Bring your digital camera and use it. This day is on my nickle so I don't feel bad at all about this, and if either refuse, then I walk.
On survey day, I and my wife show up at least an hour before the surveyor, she does aesthetics and I do technical. We then compare notes, and notice what is on the boat, what is in the listing, and what we want that is not in the listing. I have been burned in the past...broker used a "sister" ship photo, that had davits, dinghy and "all related sailing" gear. When we came aboard the second time, all the sailing gear had been removed, the new avalon with engine swapped with a no name and no engine. (about $20K difference - we walked)
I have my list and notes ready and have a chat with the surveyor first thing, I tell him what I want, confirm the price and any terms he has. We then walk around the boat, talking about this and that, I add to my notes, he does the same. By now the broker/owner has appeared and with their permission we start the engine and the genny, disconnect shore power and make sure everything idles, comes up to temp and things are nominal. IF the surveyor, I and the owner/broker all agree, the survey will continue...or it stops now, if the engine doesn't start, smokes, leaks, won't go in gear, etc, etc, same for the genny. Genny shut down.
We do the sea trial and I ask to SEE everything work. I want every sail unfurled/furled, all points of sail, backs and forwards, turns on a dime, stops. I want the swim ladder down, the anchor gear tested, etc etc. If it has a knob or a latch, it is exercised. Results noted.
If the sea trial goes well, I call the marina for the short haul (you have contacted them and explained that you plan on being there between such and such time) and ask whether they want me bow to or stern to. We head to the marina. Step ashore. I and wife on one side, surveyor on the other as she comes out of the water. We trade places. Take notes and pictures.
I then poke and look. If there is a show stopper here, or any where along the line, I or the surveyor can ask to step aside, discuss and make the call - BEFORE we haul completely. IF it looks OK to proceed, then we do so. hammer and moisture meter, sharp knife or awl for blisters. Then I step back and let the surveyor do his thing. I am within ear shot for any thing he has to say about the boat.
Once he is done, he and I talk, and with in a short time have his preliminary findings so that I can notify the owner/broker while she is hauled that I want the bottom scraped and painted, thruhulls repaired, zincs, and other maintenance I WANT done, and make sure that everyone knows it is on my nickle. Again you need to speak with the marina and make sure they can do the work YOU want done. Make it clear who is paying and who the marina answers to.
I then ask the broker for a few minutes, and say either "we are good to go and we have a deal, draw up the final papers", or "WE have some things to negotiate, when and how would you like to do that" (usually they will want to SEE the survey, so it may be a day or two to get your copy) or " I am sorry this boat has too many serious issues, such that I am no longer interested, please have my deposit and a release available by close of business" today or tomorrow - your call here.
I really try not to talk business with the owner, some are unrealistic in their expectations and you will not be happy. Some are the most wonderful people, though and are honest and willing to work with you.
Settle your yard bill, pay the surveyor and get ready to enjoy your new boat, or start the process over.
Sorry to hear the 5%, as you have said an engine could be way more than that.
keep us posted.