Advise needed on dealing over price
Your concerns are not insignificant. Boat pricing and brokers both run a broad range from reasonable to rediculous. I could not determine from your post whether you have your own broker, someone with whom you have some history and have established trust.
To the point. Its been said that boats are generally listed with a 10% reduction in mind. Be that as it may... you need to do a lot of research to find the price you SHOULD pay for any given boat. Bucnet.com and NADAGuides.com are both resources for finding fair market value. I feel that Bucnet is most accurate and is what many banks use as a guide for financing.
When the economy expanded from 1992-2000 and people had a greater feeling of wealth, used boats that had been depreciating steadily actually went up in value. This is a once in a lifetime phenominon, however, many brokers still would like to convince you that it is valid. As we all know, there has been a tremendous contraction in the past two years... unfortunately, many sellers either overpaid for boats in the late 90''s and hope to recoup that or they are still deluded into thinking that boats are worth more than they are. DO NOT be drawn into this. Market forces in the boating industry may lag a bit but they will catch up and, in general, a boat will end up going for what it is worth. If you overpay for a boat now.... YOU will be the one stuck for the loss when you try to sell.
Without specific information, it would be impossible to judge what the boat you are interested in should be sold for. Check on Yachtworld.com for comps...but keep in mind that many boats are still overpriced and it is impossible to judge condition online. Truly good boats seem to be few and far between, however, you should never be pushed into paying more than the fair market value. Check the above resources and then see how the price looks to you.
Best of luck.