If its not too late heres how I aquired mine. Had already decided on the Centaur as suitable for my sailing ambitions.
Established a base line price by serching the web and mags.
Checked out how the bid process worked by showing a bit of intrest in local forsales.
Found what I wanted and bid 15K on a 17.5 asking price previously reduced from 20k
Paid 2.5K deposit refundable if sale fell through. He was hooked but thought I was.
Survey showed gelcoat blisters, I would have been surprised if it hadn,t as I checked the hull before bidding. agreed deduction of 2.5K.
Paid over the remaining 10K, he jiped at my suggestuion he pay for an engine service. we did put her in the water at his expense for a test sail before final payment.
She had a nearly new Yanmar gm30, receipt for 7K, and newish mainsail.
I put a week between each stage and feel he would not have been so ameanable if I had appeared over anxious.
Its buisness till you are the owner, then the fun starts.