Crazy day at costco!

So I went to Costco last night to do some grocery shopping. I get everything I need and some more and head to the check out. As they are ringing everything up I realize that my wallet is missing. I know I brought it in because I have my Costco card. But I seriously can't find it. I trace my steps wondering if I left it somewhere by accident, but can't find it. I am about to cry in horror that someone stole it when a security guard asks me if I am missing a wallet. They have me follow him. Come to find out someone had stolen it. I guess while my cart was empty and I was looking at something a man had switched my cart with another empty one. A worker had just happened to be watching him. She quickly when up to him and asked if that was his. Without speaking the man left the store. I guess they were waiting for someone to claim the wallet to make sure it got back to the right person. So they had to ID me and everything. Needless to say I will not leave my wallet in my cart anymore. That was such a scary experience. I am so thankful to that worker for asking that man. She could have just turned walked away and thought nothing of it!! So just a warning to everyone, PLEASE BE CAREFUL AT STORES. And don't be stupid like me and don't look away from you cart for a second. People are very sneaky.