Notice that I called it a bit shady. I wouldn't do it, and my trust in people will be reduced if I see them doing it. But it's not the end of the world.

It's not ethical to do this sort of thing because the participants in the auction expect you not to do it. By secretly acting contrary to their expectations, you're betraying their trust. But while it should happen very rarely, sometimes you get into situations like this accidentally or due to insufficient ethical consideration. It's something I can forgive fairly easily if it doesn't become a habit.

The preceding ethical analysis is irrelevant to forum administration, though. Scammer tags are given, in general, to people who break explicit agreements.