Not uncommon really... Hasbro's made it relatively easier for people to do that with the new packaging actually.
The practice isn't the most moral by a longshot,a nd it doesn't help anyone's area to get NEW product in either. It's a definite no-no.
The employees at stores don't care though,a nd don't know what they're selling, nor do I blame them (If you make minimum wage, you can't be expected to be overly enthusiastic about your job, I'm sorry). To them it's easier to just take it back and let the store absorb the cost and move along. Unfortunately we all pay for it in the end since it's labeled theft and that factors into product pricing at stores.