It helps to know the value. I think some is sellers not knowing, and assuming it must be worth more, and some is sellers hoping buyers don't know. Of course auctions add in bidding frenzy.
I've noticed a couple of mini-lathes on CL recently ranging from barely discounted to more than new. One in particular was a nameless 7x14, seller was asking $500, you can find dozens of the exact same nameless lathe on ebay for $476 with free shipping.
Of particular concern buying used Mitutoyo is the fakes, not so bad if you buy a cheap new one that is a fake (many are apparently still pretty good, and as long as you didn't pay a new real price I guess not a bad deal), but I would worry about getting a used fake and paying a used real price (I'm sure there are people buying fakes, then selling them as used real). When certified dealers have 6" Mitutoyo calipers on sale for $111, and ebay is full of "new" ones for $49 it is not hard to imagine people are buying these, adding a little wear and then selling "lightly used" for $82.
MSI Viking 6" Mitutoyo caliper
Ebay $49 "new" Mitutoyo 6" Caliper
Ebay $82 "used" Mitutoyo 6" caliper
Not singling out these ebay sellers as fraudulent, that used one might be completely legitimate. There are a bunch of $49 ones though. MSI Viking is an official Mitutoyo retailer, so hopefully can be trusted to be selling "real" Mitutoyo. BTW they do sell used and refurb equipment through an ebay store as well.
Full disclosure I bought a caliper from MSI Viking, when I started to learn how wide spread counterfeit Mitutoyo was, yeah it was more than ebay or Amazon, but at least I know I'm getting what I'm paying for and calipers are relatively cheap.
Yep on another forum a guy was trying to sell his mitutoyos calipers and didn’t realize they were fakes he had owned them for a while and bought them from a reputable seller (I thinks travers but don’t quote me) and turns out they were fakes. Even the real dealer sell fakes sometimes not knowing.