Do any of the other items show any bid retractions? I would think it would be kind of dicey to shill on several items without exceeding the other bidders' max on some of them. Once you've outbid the other bidders' max, the only way to back out is to retract...
I think I'd report the suspected shill bidding to eBay - after all, you have no way to confirm with 100% certainty, but they do, assuming they'll follow up. Which is, I guess, a big assumption.
I don't think I'd go so far as to leave feedback based on 100% certainty that the seller engaged in shill bidding. Would probably just leave it alone. I also wouldn't go so far as to spend good money returning the keyboard on my dime if the ending price was still good (in spite of competitive bids) and the mdse what I expected.
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