anyone worked in shops and had to deal with them?

Had two in the last two days, both under my watch. Feel like a total prick.
1st one basically let himself into our office and nicked stuff. The doors in a bit of a blind spot in the shop but I was being a dozy cunt and missed him.
Just had a guy in a couple of hours ago who pocketed something in the same blind spot. Was on to him this time and was 99% sure that he did it but was busy with a customer and didn't have the confidence to pull him up about it until I'd checked the cameras, by which point he was off down the road.

Just constantly getting the piss ripped out me at work by these pricks.