value of classic DEC machines?

A putz is a putz, without the need for eBay. I know half a dozen guys on my swapmeet circuit that sit on merchandise for years, and put what seem like ridiculous prices on almost everything they have. Lots of times I will see some really curious bit at one of their spaces, but I have learned not to bother looking. They may have stuff I want, but I am NOT their customer. Joe fatwallet who has been looking since childhood for the item is his customer. Long before ebay these sellers were around, and nothing changes their minds on price, so don't waste your time. BTW the answer to your question is that believe it or not these high price sellers likely have a few customers that look for them at the various swapmeets, and cheerfully pay the inflated prices.