No, just a broker who is trying to win your business. Still going to be around £6,000 + VAT if he sells it. If you are selling a house at £250k you would be paying about 2% + VAT, so I would say he is just being sensible
No - not too good to be true. I have been offered 3% and in the past have also paid low rates like that. So 4% is OK and they will make a nice profit out of it.
The boating world is just adjusted to bad service and high charges so you will often find some breaking rank.
My very first boat sold of about £85k and I got 4% on that one from a maintream broker - I think that is the real rate in the market place on all but the smallest boats.