If you caught it, the kid in the shop also said the mod was 3.7 volts. I'm guessing he got that # from the batteries, however, if he thinks a mech is set at 3.7v he needs some education. The guy who did the video is just a common place idiot, a lot exist. As for the kids working there, I rarely feel this way, but I blame the kids dad, his boss, since he surely is the one who taught them. If taught incorrect, you will likely replicate that and do the same. When teaching someone about building, it is your responsibility to be as thorough and detailed as possible. They are relying on you, and you can't expect everyone to read forums. I'm sure his dads an idiot, and taught those kids wrong. One redeeming statement they do make is that mechs and rda's are for advanced vapers only, and he even states that it's when vaping becomes a hobby, both true. They sell one to a complete idiot still, though.
I'm not excusing their actions, I've been told to use icr batts by a store owner and all his employees, he even showed me a sub ohm build that he runs on them. I left without making a purchase... I hope he doesn't cause anyone to blow themselves up. It's unfortunate that these idiots are in shops, if they were just taught properly, I think they'd be ok. Problem is, one individual taught improperly can snowball into a ton of people once they teach some people themselves. I do feel it's common sense to do your own research, but we all know that common sense isn't so common. I started building with a kayfun and my mvp, I didn't mess with mechs until I was a couple months into building and comfortable with it. Additionally, I educated myself, since I knew next to nothing about electricity. I don't fuck with shit I don't understand, so I read, and go to shops that are legit.