What causes decks to warp? Moisture? Pressed incorrectly? Too much / little glue? Stacking?
Don't think I've ever skated a warped one and wouldn't be able to tell if I got 1.
More often than not it is from heat, or incorrect storage, but I feel like there must be something in either the process or the wood itself that tends to cause more issues.
Often boards left on the wall or in shop windows, especially sun facing, tended to warp more than others, but other times, it is just seemingly random that quite a few boards from a run will warp more than others.
To stand on a warped board, or even putting on on a counter, it will tilt more one way than the other, or if set up, one wheel is often off the ground, when trucks are in a normal position. Most of the time it is not so bad, but some boards will definitely feel weird if they warp a certain way for how you stand on a board, eg front heel side sitting up more than the toe can be the worst one.
People will often have different ways of dealing with it, but I offset a board on a flat surface, like a garage, with small pieces of wood, then weigh it down under other boards and put bricks on top and leave it for a week, which pushes it the other way and evens it out. I have had almost all the boards come back to straight or almost straight from this and skated well, but some just can't be helped and will warp back again in no time. They are the ones I think there was something in the wood that makes them do that, more so than an environmental factor at play.