They are awful. I used to work at a real auto repair shop and we got alot of work out of fixing Jiffy Lube's F-ups. Stripped oil pan drainplugs are common. Some Honda vehicles require a special type of power steering fluid, and I've seen them put regular ATF in there and destroy the power steering pumps on those cars. Certain Ford vehicles require a newer specification transmission fluid (Mercon V) and they've put standard fluid in there.
I've seen them do the double o-ring on the oil filter. This is when the o-ring gasket from the old filter is still stuck to the engine block and they crank the new filter on. After a short time, the extra o-ring blows out resulting in a massive oil leak. And yes, I've seen them drain transmission fluid instead of oil and pour oil into a transmission.
Saturn vehicles have a spin-on filter for the transmission which looks like an oil filter. I've seen them change THAT filter instead of the engine oil filter.
The list goes on and on.