@TinyJazz, that's not an official rule lol, it's just a personal observation.

Basically, from my perspective, unless you're really careless with your Transformer toys and break them/or lose parts, why would anyone need more then one of each character?
It's a sad story, but I know a friend of mine had a violent encounter with a scalper and ever since I heard their anecdote, my tolerance for anything like this behaviour is gone.

Also, I don't remember where I saw it, but one particular store (I think it was EBGames) actually had gotten smart about scalpers and basically said to their customers for the more valuable collectors' items, we're only selling you one, if you try to buy a second one, we won't let you have it.
So for them, it was an official policy.