You are allowed to bring into US $800 duty free stuff when you enter US as an American citizen. If you are with a hubby or a child, you can bring $1600 worth of stuff without declaring it. Basically each person gets $800 pass. Naturally you can bring over 10k worth of stuff back to US and not declare it. That’s up to you. But if you get caught you will be fined and after that every time you come back into US you will be checked. So whether you want to declare if you go over the limit is up to you and it’s the risk you take.