Interesting. From the same data set I had, I could fit the list price against the production year of the boats. That produced a positive slope in the list price by production year of approximately $14,000. That, and the inference that list prices are, on average, greater than the corresponding sale prices, is an unremarkable result (most sellers hope for a naive buyer who will pay more rather than less, relative to the seller's perceived value of the item; as most things age, they lose value). The actual level of the trend in list prices, by production year, is, of course, uncertain, but it is reasonable to me that the older a boat is, the lower its value, on average, in general.
Before I provoke more comments about the uselessness of analyzing such data, here are some more caveats:
1. Of course the right price for any transaction, whether for sailboats or tomatoes, is what a particular seller and buyer agree upon for an exchange of a particular boat or tomato for a particular amount of money, but in my opinion, a prudent buyer would attempt to find out what other buyers paid for their boats or tomatoes, and how the price paid related to the buyers' expectations as evidenced in their list prices. But that's just me;
2. The data I used are a sample of the transactions over the past ten years on a particular make/model of sailboat. The results in themselves indicate a range, rather than a highly reliable fixed point. If the same analysis is applied to other boats, or to a different sample of the same make/model boats I am interested in, the results will most probably be different. I have not suggested that there is a fixed and reliable rule across boat purchase transactions for the relationship between list and sale prices which should determine what a potential buyer should offer relative to the list price for a particular boat. That decision requires more data and information on the specifics of the boat, and the circumstances of the potential sale.