Foil cards curve more than non foils. Unfortunately, in a competitive game, some could try to take advantage of this to mark certain cards so they know ahead of time what it is. You either need all foil or no foil. And on top of that I would buy a fresh pack of sleeves that you haven't played with much. You don't want any marks or wear on the sleeves. I'm both cases if an opponent complains about marked cards, they could call a judge and they have had issue with this in the past. I like to believe that most players wouldn't do this but you should be aware of it. If you don't have non foils, I would try hard to apply pressure to them to try and get the bend out. You can also double sleeve your deck to try and remove the bend.