I have done some Buy It Nows... most of the crystal/mineral
sellers (but not all) have a store. The store tends to be a bit more, but sometimes that is the best way to get an item.

I do think I have seen some shady things...you know people
bidding who are shills...but that is so hard to prove.
So I just ignore those sellers. What I do is go back to the
feedbacks (I keep the item on my screen for a month or more)
and see if feedbacks are given.

Twice now I have received Second chance offers, and both times where I was out bid, those offers seemed contrived.
It was like the shill bid up, then I dropped out, then next thing I know I am getting a second chance offer for my high bid.
I don't respond to them. I have found some times no feedbacks are given on items I've lost. Ebay I think says you must accept, but I have not, and no one forced the issue.
That also made me think it was contrived.

I used to search those people bidding against me, but since they put that anon feature in, I can't do that. But I will search the winner after it closes. By searching the feedbacks of the winner, I often find stores and other sellers with similar items that did not come up on searches.

Sometimes I feel like a detective! I am sort of that way anyway so it fits for me. LOL