Boxes not in bin I scanned them in

So its my 3rd week and im a stower. I was brought up to our OM about a few boxes I scanned aren't in the bin I scanned them in. Apparently im not getting written up, just a standing lesson for now. But I wonder what's stopping someone else from moving boxes around so they can stow there's and not putting it back in that bin? I'm always scanning the right bin but they said next time it could be a write up... im a seasonal badge trying to get to blue ASAP but this feels like a set back. Any ideas what I can do?