I worked at a mall in the 90's in two different stores. One was a clothing store, and 'home shoppers' made up the majority of the thefts.
The way it works, is you 'place an order', and someone from the theft ring steals what you want, and in a few days you get your items at a discount from the 'home shopper'.
I remember my dad would buy some random clothing items from a friend of a friend who had things in the trunk of his car. I never thought much of it.
When I worked at JC Penny I then saw how it worked. You'd have random individual shoplifters (they'd leave all the tags and stuff from the clothes in the bathrooms or dressing rooms), or you'd have multiple shoplifters come in at once, fill their carts and then dash out the door, getaway car waiting for them.
Store security couldn't do much, if you tackled the people you'd get fired, so the best defense was to jam up the automatic doors with empty shopping carts, that way they could only leave with what they could fit in their hands.
It wasn't much different at the electronics store I worked at afterward. PC add-in cards would end up missing, empty boxes found in the appliances on the other end of the store, sliced open so they could be fished out the bottom. There go the new $300 3Dfx cards...
And the organized shoplifters came in at night, just before close. You'd have 5-6 people come in, and all head for the CD aisle. We'd page for customer assistance, and anyone still working in the store would head over. They'd fill their coats with CD's and again run out the door, getaway car waiting.
All you can do is get them on camera, record the description or license plate of the car, and let the police know, and let the other stores know. Our internal email system had a ongoing thread of the shoplifters they'd seen lately, because they would hit every store in the state.