First, State registration can be a problem. Other countries don't understand it and therefore, don't accept it. Especially France - I don't know about other countries.

Second, there are Recreational Craft Directives in the EU. They concern the EU's version of safety regulations. Unless the boat has sisterships already European certified their laws prevent the vessel from being used. It can be a huge hassle and expense to get an older vessel certified - far exceeding the cost of the vessel.

Next is VAT - value added tax. In the UK it is 17.5% and must be paid when sold in the EU or if you stay there longer than 18 months (I think 18 months). Some cruisers have successfully avoided this by importing it as their primary residence. I doubt that would apply if it is sold. BTW UK VAT is among the lowest in Europe.

How big is this boat? I thought all vessels over 10 GRT had to be documented.