Reserves allow a shadow bidder to run bids up without getting stuck with the sale.
Set a secret reserve price of $2000......shadow bid to $1999.99. If the legitimate bidder doesn't bite after that......the sale is not completed.
It is only dishonest if the shill somehow knows what you maximum bid is.
As long as the shill has the chance that you will drop the bid in his lap, it is an honest auction.
Are you accusing Gunbroker of bidding against you, up to one bid under your max? Or possibly accusing Gunbroker of informing the seller of your maximum bid?