Our local machinist's club the "Southern Arizona Model Engineers" had a member who has dealt in used machine tools for over 30 years. He has given his "Dutch Uncle" talk several times, regarding liquidating a shop.
He says he can only offer about 1/2 of what it is worth. He has to move it, store it, possibly repair it, and still must make money on it to stay in business.
His basic advice is to liquidate your shop BEFORE you die, as your heirs will have NO CLUE about value. He also said that you should not sell to a machinery dealer, while expecting full price, because it simply won't happen.
His recommendation is to sell it yourself if you can, with the proviso that whoever buys the item must come and pick it up. He stated that this was the only way to get full value for what you were selling, and it only works if you realize and understand the value of what you have.
But basically, the resale value of used machine tools is pretty low. Because they are generally heavy, and hard to move, high asking prices will result in the machine going for a scrap price eventually after the heirs realize that absolutely no one is going to pick up their used Bridgeport, and pay top dollar while doing it.
He HAS bought estate machinery, after frustrated relatives found out how difficult it actually is to liquidate this stuff. But he stated that the best way is to sell if before it becomes a problem for your heirs to solve.
This individual has an excellent reputation locally for honesty, fair dealing, and he also will deliver and set up any machine you buy from him. (That's a pretty big factor! We had one local member who had to have a leg amputated after a milling machine he was moving tipped over, and put the milling rack rod through his lower leg. (Twice! They had lifted it up to get it out of his leg, and then it fell again, and went back through the leg a second time. That constituted a VERY bad day!)
When I had a 10" X 54"Mill delivered from ENCO years ago, I had it dropped of at the machinery mover's business, where they could unload it properly. Then they brought it to my house, moved it from the street, taking it off the semi, moved it down the alley that gives access to my backyard shop, rolled it into the shop, and located it perfectly. It took less than 15 minutes from the truck horn to when they truck pulled away. The only thing I had to do was carry the paper machine manual with me from the street to my shop. I also had to plug the machine in. They did everything else, and it was well worth the $300 they charged. Sometimes the skilled trade is easily worth the money you spend.