I'm not sure how others feel but I think asking for DT is questionably shady akin to asking for positive feedback but I have not come across a conclusive discussion of that matter.
I think it's shady. The only other person I recall doing this was Quickseller when Blazed was expanding his list.
It's not dishonesty or scamming for auctioneer to bid on an auction. Many people agree with me on this, including theymos. This is also very normal in auction houses in Finland. Are they all unethical scammers?
It's dishonest to do so without disclosing such possibility. You've been told this numerous times but you keep omitting this part.