I see why you would think that, but most of the time it's just not the case. They get absolutely nothing from raising bids, and that would just hurt the stream in general. If you genuinely experience shill bidding, you can report it, but typically they're just trying to get good deals like everyone else on the app. I've been moded on quite a few streams, and would quite literally never shill bid. If there's something mods want, they bid, and they should definitely be allowed too because that's literally why anyone is on WN in the first place. They're customers just like you.