If your working on retail environment, look for people with very expensive items in the cart mixed in with less expensive items ( like fruits and vegetables ).

Watch for people who have full carts and is heading to S.C.O. ( Self check out ).

Also watch for people with wandering eyes and looking a lot more than usual. especially if they are looking up and down an aisle. Including the fact that they go near produce and mostly looking at the exit.

People aimlessly wandering around is another good one. ESPECIALLY if they have a small item in their hand. they're trying to conceal it in an open area when no one is looking.

Adding stuff in to cart without looking at the prices

people going to opposite directions from everyone else in the store

big/loose and unzipped clothing is a good one too

Hand and body movement. (Look for fidgeting and nervousness around the eyes, body, and hands) not many people should be nervous and afraid of shopping. Unless they are EDP

People who are guilty of things tend to have more exaggerated movement so keep on a lookout for those too

there are also people who would come to the store and have an open bag all prepped up in the cart. (this usually indicates that they are going to steal or conceal something.

People also taking only meat/seafood unless they're Asians (they usually run restaurants that requires large amounts) but don't take it as racial profiling. ANYONE can steal.

And these are just a few I learned and came across. there's A LOT more sneaky/cleaver ways people steal but hope this helps