I haven't had anything that bad happen, but............I needed to get an oil change a few weeks ago, and Wally-World does synthetic oil-changes in our area for about $35 with tax (Your choice of brand).
1st, I get there at 6:50 in the a.m., since they open at 7. In theory. At 10 after seven, a woman drives up, asking if they've opened yet. I tell her no..........not since the last time I checked the door. I decide to turn the Libby around so I can see better, and they open the door while I'm doing this. So, the woman, who KNOWS I've been waiting 20 minutes, walks up to the door and right up to the counter. Bad etiquette on her part, but hey: "You snooze, you lose" it shouldn't be THAT long, all she'll do is get an oil change, right? Wrong. She proceeds to take up the next 15 minutes, finding out which tires she should get and if she needs 2, or 4. (Meanwhile, the mechanics are twiddling their thumbs).
When I get to the counter, I tell the guy, I wan't Mobil1, 5w30, and I have a half-quart in the Jeep, for when they fill up. Now, it's 7:30. At 8:45, I go to check on the Jeep, since I haven't heard anything in almost an hour-and-a-half, and see the mechanics putting in GOLD colored bottles of oil? I step outside, and check with the mechanic - his response is, "We dont have any Mobil1 5W30, this is Pennzoil synthetic BLEND, and he told us he'd already asked you if it'd be OK". (It wasn't - I have nothing against Pennzoil OR synth blends but I ASKED and PAID for MOBIL full synth).
The 'manager' that was originally there, two hours earlier, has taken off for a break. The manager on the desk made them drain it out, got some Mobil1 10W30 off the shelf, and refill. All under my watchful eye.
Long story short, I got an oil change AND an oil flush.

And no, they DIDN'T charge me extra. Maybe the 220+lbs. of 'ticked' off Jeep owner kept them from trying..........LOL