His suggested price was 1/3 new. At an auction, I cut my bids off there .
This is similar to how I think.
It's worth expanding the idea a bit.
I will NEVER pay new prices for used. Warranty, support, parts availability, etc are all worth something.
1/3 of current new is a good starting place. So is 2/3 of original cost. Inflation can't be ignored, but neither can depreciation. Together, these two numbers set a baseline. From there, I adjust for wear, availability of parts, cost to repair, availability and cost of missing parts, functionality vs new today, etc etc.
Risk is another huge monster. Even if the seller knows there is no risk, the buyer can't assume that. There is no universal perfect formula.
Another important factor is timing. Can you afford to wait for the perfect buyer? Priced to sell is a perfectly valid approach. So is waiting for the right deal - on both sides of the equation (buyers and sellers).
Anyway, the 1/3 2/3 guidelines are a good place to start and then adjust for other factors. It's how I think about what I buy and sell.
Last but not least, the market is the market. What I think doesn't really matter if the free market says otherwise. What is machine ABC really selling for today? Not what is being asked, rather what is actually being paid.