AFAIK he's using RatScanner[1], or something like it. I'm pretty sure the admin of RatScanner is in the Discord quite a bit, but that could be a coincidence (but I think it's some form of image processing lib no matter what, they include a screen cap of the latest market info for an item on the page when you pay).

I'm not sure I would consider what they do effective in banning trade bots (the captcha seems ridiculously easily beaten), I think the Found In Raid object flag is probably the really effective thing keeping most bot usage down, since it attacks the actual incentives of using a bot (it's still useful to auto-buy when markets dip or someone under lists an item, but that's about it I think, but I may be missing a use).

That said, if all you're doing is scanning the market results and not buying anything, it's probably much easier to not trigger any problems with the devs. The market data is really useful for those that like that sort of thing, but it's not really that much of an advantage, just a way for those into the economic portion of the game to go deeper.

1: https://github.com/RatScanner

It’s all done just by image processing. Once premium you can see the screenshots of the items on market used to provide the price estimate. They must have a couple accounts running continually going through the market checking prices. That’s why some items are 2-3 hours delayed.