"Shop fees"

Or wait until your shop does a multi-thousand dollar rebuild and the customer either won't pay or wants to pay it off a piece at a time. Under our state law a mechanic's lien is a possibility but by the time you wade through that process you're still left with a customer who can't or won't pay his bill. The cheap-skate SOB comes around whining about how bad things are and we charge too much and he's in serious trouble and then he drives off in his wife's new Escalade.
If you're lucky you can sell the truck for enough to recoup your costs but it's a lousy way to try and make a profit.
Our shop solved that problem by never getting in so deep on repair costs that a lien wouldn't cover everything. That, and hardly ever working for somebody we didn't know. Our company trucks came first, then the outside customers.

 

It's true, a bigger shop can absorb that and we're big enough not to get stung too bad. But that isn't the point. The shop, just like the trucks, or the Cats, or the fire wagons, has to show a profit on a fairly continual basis. If you get a slow time or a no-pay time it takes awhile to make that back up. The people the shop uses for vendors don't cut us much slack on payments.
Luckily I don't deal with the shop end of things too much. Our chief mechanic is good at keeping costs in line and he's been here longer than I have and there's no need for me to ride him about anything.
The P&L statements come across my desk every month and there's usually more green ink than red. I pass the statements off to the bean counter and she does what she does best which is double checking the figures, paying off the bills , and otherwise giving the whole thing a good leaving alone.