Can a seller bid on his own item
No.
That is "shill bidding", and a felony in most states.
eBay also tracks bids, to help assure sellers do not bid on their own items.
This is not to say that some sellers might find a way to do that, but there are lots easier (and less dangerous) ways to make money on eBay.
AND, shillers do not bid to win! If sellers won their own items, they would still have to pay eBay fees, unless they gave themselves nonpayment strikes. It is LOTS easier to start the bidding at the minimum acceptable price, or place a Reserve on the auction.
A great place for quick answers; no waiting, no voting,
"Do It Yourself": eBay Customer Support .