It's not hard to tell if a pump's bearings are going bad and it only takes a few minutes. The pump needs to come off so the flange can be turned in the person's hand. If there's any grinding or vibration, it's going. If it's smooth, it's not. Might have a bad seal, but the bearings aren't necessarily going bad.
Discuss this calmly with the dealer/service department. I think it should be part of a marine survey, but not all dealers and service departments do these the same way. You'll need to look at the contract and see what recourse you have in this kind of situation. If the boat was sold "as is", your position will be determined by where you live. Do some due diligence to arm yourself for any discussions with the shop and dealer. If you don't know your rights and responsibilities as a consumer, at least find out what the dealer's rights and responsibilities are.
With cars and land vehicles, the power train has to be in good working order. The cooling system, being part of the engine, is absolutely part of the power train.