Are you talking about an auctioneer that doesn't own an item legitimately purchasing it from an auction for themselves? You are the seller, you bid on your own item. Its shill bidding.
Talking about an auctioneer who owns or doesn't own the auctioned item. Legitimately purchasing it from the auction for themselves. The auctioneer is just the technical operator of the auction and has no say in how the auction rolls. Therefore he's on the same level with other bidders, he has no decreased or increased position to act as a bidder too.
The word "shill" itself refers to something being done in hidden. Nothing was done in hidden in my auction. There was no attempts to falsify bidding activity, which is what shill bidding is.
Also:

Also:
Here's something related to this:
https://mikebrandlyauctioneer.wordpress.com/2010/08/24/can-the-seller-bid-at-auction/Therefore, if the seller bids then a reserve has been placed on the property selling thus the auction would have to be a with reserve auction, and not a without reserve auction.
The default in U.S. law (if that interests someone) is that all auctions are
with reserve. More about this earlier in this thread.