by ravenskana
Well, my thoughts on it were that some special building is going to come up anyway. Moving A and B to the bottom of the stack is a risk, as the C card that does come up could benefit anyone and you didn't get a chance to see it.Also, the A and B cards aren't out of the game. Nothing stops someone else from using Marketplace to keep dumping the new A and B cards to the bottom to get the original card you want to the top.
It seems like the only way it can really mess you up as described is if after seeing A and B and putting them on top of the stack in any order, you start making plans towards both of those, then another player moves them right before they get built. And again, while some of the work the first player did might be considered wasted, the second player may not have gotten any real advantage, so who knows.
I've also found Marketplace to be fairly strong just in the goods that it gave with the knowledge and manipulation of the cards a large bonus. One could argue this wrong way of playing might depower Marketplace slightly, so if that's a goal, then it wouldn't hurt to try it for a game I suppose.
It also occurs to me if one wanted to play the way I was mistakingly playing, play with the exact number of cards in the deck that will be used in the game. That way, moving to the bottom of the stack will always delay the card rather than remove it from the game (given no additional player interaction with the stack).
Finally, on a personal note, almost all of my games have been with my family, and in particular, I usually play three player games with my two boys. A houserule we have is that I deal each of my two boys a number of special cards in the beginning of the game, and they each draft three cards to place in the deck. The six cards are then scrambled and put out. This way, they each know half the deck, but not the initial order, and I don't see any cards so I have no knowledge until I use the marketplace. It could be that under this configuration my mistaken play of moving cards all around the deck was less problematic, well, except when they did it to me but that's a handicap I was happy to play under.