What were B&M staff doing when they said they were “Doing the Cars”?

I was in B&M this morning just after opening, I was at the checkout and 4 members of staff walked past and said to the checkout lady "Just doing the cars Tracey!"

They walked outside, when I got outside, they were going through the boot and back seats of a car, while one of them was looking over and writing on the clipboard.

They were walking to a second car by the time I'd got in my van and started driving away.

I was sooo close to pulling up and asking if they'd tell me what they were doing, I'm regretting not just asking.

Were they checking staff cars for stolen goods or something?

Any B&M staff or retail staff in general heard of "Doing the Cars" or car checks before?