I think your overthinking it, I've had people over the years make a new account because they liked a player and just bid on several cards like that, they are new and want to make a collection, I sell cards in bulk of one player like that alot of times as well. definately doesn't mean it's shilled. but at the same time it could be? I guess if the card goes too high just leave it alone is the best option, that's what I always do. I just pick my price and if it goes over someone else gets it, easy solution.
Collecting Carlos Correa / Byron Buxton / Manny Machado / Bryce Harper / Mark Appel / Kris Bryant (lower end stuff & bgs slabs) Basketball: Blake Griffin / Derrick Rose / Paul George / Damian Lillard Football: Andrew Luck / Russell Wilson