I When we were looking for a boat recently there was one broker (can’t remember which one and they may have changed their terms by now) who said on their website something along the lines of ‘ if you make an offer under the asking price that is accepted, and the survey shows work required, don’t expect a further reduction if the work required is less than you already have got off the asking price because you have already had £X off the asking price’. That broker had a 10% deposit scheme and it was up to them to decide if the survey report was significant enough for a reduction in accepted offer. Basically they had your 10% and you were not getting it back so you might as well carry on and buy the boat!
I wouldn’t even look at their boat sales adverts.
eta - just checked, it was, and still is, Nationwide Boat Sales (formally Great Haywood Boat Sales)