Wait till you bring your car in with your own (expensive, boutique) oil for a change, find the lube tech dumped in cheap bulk oil and the put the good oil in the trunk of his car. Then the dealership service writer (not the one who originally wrote it up) tries to charge the car owner for the oil and deny he brought his own oil in (on the tech's sayso). It all fell apart because, a) the car owner saw the tech carrying his oil out of the shop, and b) the service writer who wrote the original ticket wrote "use customer supplied oil." In the end, it was a pretty embarrassing event for a Toyota dealer, the lube tech went job hunting, the second service writer had some of his rump surgically removed (for being a complete dumas, I suppose) and the car owner (a friend of mine in California) was given a bunch of free service coupons.