I think $35k is probably a fair price when considering the cost of the yacht when it was brand new, what it would cost to build it today and it's age.
If it is in absolute pristine condition with all the "gear", it is probably a snap.
If it is run down and needs this and that fixed and no effort has been made to "present" the yacht, it is probably some "silver tail's toy" that he can no longer afford and he wants to dump it before it costs him too much more.
If that is the case and it is the yacht you want and can handle it physically and financially, bust his arse and ego and offer him $20k or less and state that the offer stands only for the next 24 or 48 hours.
It is a difficult question to answer. Sometimes you have to take your gut in your hand and punt. Are you ready for that??
The other thing is to never ever forget the first unwritten rule of yacht ownership.
That is:- "Never let the value of your yacht/boat exceed 10% of your nett worth and never let it's ongoing cost of ownership exceed 10% of your income."
So, if you are prepared to accept that rule, get a sheet of paper, rule a line down the middle and a line across the middle.
In the top left quadrant, list your liabilities. In the top right quadrant, list your assets. Subtract liabilities from assets to determine your nett worth.
In the bottom left quadrant, list your monthly expenditures. In the bottom right quadrant, list your income streams (it is great to have several). Subtract expenditures from income to determine what your disposable income is.
This is what is known as an "A & L, I & E" statement. If ever you seek a loan from a bank or finance company and they do not require one of these, you should walk out and seek money elsewhere.
I do one of these statements on my self on a fairly regular basis (annually is good) just to see how I am travelling by comparing with previous years.
If you only have $35k I don't think you should buy this yacht or any other for that price. Think about a great design sailing skiff for $3,500. It will be more fun and probably sail faster than that yacht. A "Flying 15" is a great choice as they were the first of the planing keel yachts. I was partners in one at Yowie Bay in Sydney and we had a ton of fun with it. Good ones are worth about $6k though.
I hope this free advice (advice is only worth what you pay for it.

) is of help in gelling your thinking.
The above is only my opinion and there are others who would totally disagree and say "Just Go For It!!!". That has worked for many very successfully.
In the end it is your choice. If you WANT it and can afford it, you should have it.
Cheers Cisco.