Treat them with caution - a friend selling his tug style nb sought 'opinions of value' from surveyors, and brokers, (a well known one in the Midlands suggested £20000, before increasing this to £25k), most opinions were, no demand for such boats, tricky to sell.
He placed a £7.50 advert on the 'Duck', asking price £42K, it sold to the first person who came to see it, ..............
The key to an easy sale is to get all the paperwork to hand, have a thorough pre sale HULL survey and have the boat blacked and make sure it's well presented.