The upcoming Captain's Auction is typical if you look through the catalog. Tons of video games and things like Skeeballs and pool tables, and a pretty good selection of pinball machines. (these are typically toward the end of the listings for some reason, but there are some scattered throughout). Sometimes they will have an auction more focused on pinballs and there will be quite a few.
There have been some purchases made by Pinsiders where they were satisfied with the price, but not too many. You could ask o-din (a SoCal local) about it, but I think he is banned at least for a while. I believe he bought one at the last auction that he liked.
But in the end, you have to know what it is you are bidding on, and figure out what you are willing to pay (calculating all fees), and not go over that. But isn't that true of any auction? It has been stated a lot that the sellers are allowed to bid on their own machines, and do, which I guess is probably true. In the end, the same rule applies, know what you want to spend and don't get caught up in the bidding.
For something like a pinball machine, the online-only thing is kind of a bummer. You just have the pictures and their short description to go by. Before the pandemic, you could go over there before the auction and check everything out in person and even play the machines. I did this a few times, and enjoyed scoping out all the machines, and I went to a few of the onsite auctions. That was pretty fun to see how it all works. I never did buy anything there though, but that really has more to do with my lack of space than anything else.
Just another side note, if you stick with the Pinside NorCal group and are patient, eventually you should be able to get some nice machines and good deals. Even more so if you extend to SoCal. Over the past several years, if I wanted to spend the money and had the space, I could very easily have a collection of a dozen or more machines, all bought from local pinsiders. All my favorites too. You just have to be patient and keep an eye out in those threads. There are always TZs, TAFs, Metallicas, plus many others, T2, Firepower, the occasional Tron, and many nice EMs I could have bought. No Fathoms, but there never is a Fathom anywhere....