Having participated both as a seller and buyer in antique auctions for 30+ years, I've seen the good and the bad with auctioneers. The good usually have merchandise that will generally sell itself without any tomfoolery. If an item isn't receiving bids it should bring, they will plainly announce they are withdrawing the item for that reason, first asking the owner, if present at the auction what they desire to do, and if not present using their judgement about protecting the seller. Sometimes that will stimulate the bidding for those who were holding back. They will announce reserves, if there are any, and start the bid at the reserve. They will announce when they are bidding a "left bid" by phone/or by written bidding whenever/as they are raising a floor bid. And, I've seen them shut off floor bidders that they know are shilling or just running up a competitor in the retail business. On the other hand, I know of auctioneers that use "house numbers", up to
three or more, during bidding to drive up bids. Often on their own merchandise and sometimes on consigned merchandise from sellers who will "work with them" on that practice. If it doesn't sell to a "real" bidder/buyer, it usually holds over until a later auction. I've also known them to use "shill" bidders (at their auctions and competing auctions). They are also not bashful about prodding bidders unabashedly. If they have an item with a reserve, they will rarely announce it unless they fail to get to and beyond the reserve by whatever method they may try. Inexperienced buyers can easily end up over-paying from unscrupulous auction houses. These houses don't usually survive for long. Now, for both types, there can be the non-paying buyer and the buyer who wants out of a bid for undiscovered flaws, even though they have had time to examine items, sometimes the flaws aren't discovered until after items have been brought out away from tight packing (think furniture), and other reasons. Good auction houses are pretty good about working with you on that; their reputations is important. The bad houses; it just depends on what the issue is and the argument as to the outcome.
I've not been to a stamp auction and am not trying to "paint" any as being anything other than "above-board" in their dealings; just throwing out some things I know about auctioneering in antiques that might apply--or might not. I would think that the stamp auction business, especially with the more national houses, would be trustworthy, but "experienta docet".