Yes… they CAN . It happens all the time. It doesn’t matter what computer you’re using, just the IP address. I can use my same laptop to sell on one account, and bid on the item with another account, and I’ve got a better chance at getting away with it if I do the selling and the bidding from different IP’s.
I’m pretty sure shill bidding is not “illegal” as said by MollyMcguire. I never heard of cops showing up to arrest someone because they packed a few extra bucks on their own auction using that process.
Needless to say, it IS against ebay policy and you could be banned for doing it. Shill bidding isnt just used to drive up a price. It’s also used to buy an item yourself that wouldn’t have sold at a price you were hoping for.
Your recourse is to openly post about the item and the seller in the ebay forums to get community feedback and advice on ebay. You also want to report the item, and the seller for what you think is going on if you’re pretty sure. They’ll help out and get to the bottom of it (hopefully)