I hears ya. I worked for Tandy/Radio Shack several times between '68 and 2000 but the time I remember most is from '80 - 84 when I was going to computer school.
One of the big sellers was those under-dash auto power boosters with built-in graphic equalizers and two and three way coaxial 6x9 speakers. The boosters were rated for about 20 watts and the speakers were rated for somewhat higher, I think 50 watts..
Like you say, they walked out grinning but, like clockwork, a few days later, they would be in screaming the tweeters blew out. why? They were rated for 50 watts but the booster only puts out 20. They want a new speaker. This was constant.
Invariably, the eq was set in the ubiquitous "smiley face" configuration and they cranked those things to eleven!!! some of the smarter ones learned that when you drive an amp into hard clipping, it can send tremendous HF noise to a tweeter and fry it in a matter of minutes. This was explained to them and some actually learned from this. At one point, we explained this when we sold the stuff but still some would come back.
We would replace one speaker. After that, they were on their own.
We taught a lot of people about what happens when an amp distorts and some of those kids still own the last equipment they bought almost 30 years ago (I left that store in '88). I had one kid come in with a pair of Jamo J101 speakers that had most of its drivers blown. That model had poly-switches, which were there to protect the mids and tweeters and he still killed them. I explained that blowing more than one driver is considered 'abuse' and that we'd have to charge him for the repairs. His dad showed up, extremely PO'd, telling me that we were dishonest, it was illegal, his kid doesn't crank the stereo that loud and "wait till you hear from my lawyer!". I told him that I had a pair of that model, two of the others who worked there had them, a lot of our friends had them and that we had sold literally hundreds of pairs of that brand without a single one coming in with that much damage. He calmed down amazingly quickly after I asked "Are you at home, all the time?" and said "Let me know when they're done".
That was the time to teach the lad a lesson (he was there at the time) and I explained that full power isn't achieved when the volume control is at WOT, but closer to 1:00 on the dial. We were the second Jamo dealer in the US, so we had a lot of leeway WRT honoring warranties when we wanted and we covered the repair.
About 5 years ago, I was at Summerfest and during a break in the main act's show, I went out to get something to drink and heard someone ask if I was Jim, from that store. I turned around and he introduced himself, saying he used to hang out with certain people and when I couldn't quite figure out who he was, he reminded me about the blown speakers and I immediately knew who he was. He just hung his head when I said "I remember you!".