When one of them acts a little suspicious, we run to the back and keep an eye on them through the security cameras and, as soon as we notice them placing an item in a bag or under their coat, we rush back to the sale floor announcing to them what we just saw them doing.
At this point we usually ask them to give us the item in the bag, then we ask them to leave the store and never come back.
I feel that we are actually being nice: we could call the police and have them arrested!
A few days ago, I noticed a lady in the store who was caught stealing in the past: maybe she thought we forgot about it?
I approached her and reminded her that she was not welcome in our store.
She responded that she had a twin sister and I probably was confusing her with her.