In my view a clear example of a scalper would be those groups of people who set up bots to acquire the entire stock of PS5s seconds after it hit the stores, to sell it for 2x, 3x the MSRP. Not only they don't add any value to the production/distribution chain, they are actually a hindrance as stuff like warranty and manufacturer support can become compromised if buying from these people. I'm not a law expert, but that's definitely not "free market", in fact I don't think there would be many objections if it was made illegal. I know a big part of the problem is the inability of some people to exercise restraint when buying new shiny toys (FOMO as they call it), but I think it's not healthy (even for the manufacturers) for the market to be completely disrupted by a few people with more money than they know what to do with.
In that sense, I don't think that is a problem with the retro market, at least not at that level. What is special about the retro IBM PC compatible market in particular, even when compared to other retro markets (such as consoles) is the wild range of prices for the same type of item. So it is really difficult to determine what the "market value" of an item is (unless we're talking about actual collector stuff, i.e. NIB 3Dfx cards, actual IBM PCs, and so on). Here ignorance of both seller AND buyer plays a big part. This leads to a lot of randomness and confusion, it's not like an NES which everyone and their mother know what it is. When you deal directly with a fellow enthusiast/collector usually price ranges are much more sane, but for many people eBay is the only viable way to acquire this stuff, so they fall victim to the craziness, and as I mentioned on another post the ability to list things indefinitely for free has caused lots of these randomly priced listings to pollute the search results for years.