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.
I like to buy cards for alot of money so I can sell them for a little bit of money......