A sealed box at an auto parts store is supposed to contain a new part. But when one Mazda owner stuffed his filthy old cabin filter into the box from its replacement and took it back to AutoZone, he exposed something that got auto parts workers in their feelings.

The viral clip from creator @psychodaddy69 was one of those bits of humor that wind up revealing some hidden truths about auto retail life. Some commenters said customers really do return used parts, creating a guessing game for the next buyer who may wind up paying for equipment with no remaining use.

“People really be doing this, they leave their old one in there and take the new one. When we sell it it’s used, customers come back upset at us,” one commenter said in the clip that’s been viewed more than 116,000 times.

The Dirt On Air Filters

The trip had started with a fairly ordinary setup: the creator went inside an AutoZone looking for a cabin filter for his 2016 Mazda CX-5 that might help the ventilation system breathe a little cleaner and easier.