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I think that have 1 UR per box is a good thing. I see how it could be abused, but then you should know the person you buy your cards from. The only places you can really buy this game is from trusted online sources (like cactus or threelions)or from people you know who probably taught you the game. If you can't trust who you are buying cards from, don't buy them.
Although it's easiest when the number is 1, this can really be done anytime there's a known "maximum" number of URs per box.
If you can't trust who you are buying cards from, don't buy them.
I saw a video of someone opening a box of pokemon packs. the way they are ordered, you can predict which packs have the foils and rares and ultra rares etc. this is a way that some game store owners have used in the past, and the just take the expensive cards and sell the rest as single packs or put a bunch of garbage packs in a box and reseal it.