Isn’t disabling bad blocks of memory chips and selling them at the lower capacity pretty common?

They’re doing that too. The real problem with these is that they misrepresent the storage size, and the firmware is set up to lie to your computer about the storage size. You can format it and it’ll seem normal. Maybe you buy one that claims to be a terabyte but only stores 100 gigs - you’ll see a terabyte in there. You copy 110 gigs or so over, you’ll see the files show up and it’ll tell you it successfully copied. No error messages, it'll just drop those last 10 gigs. There’s not really a way to notice without using a read/write program to fill every block.

It’s a shitty way to lose your data, and you might not notice until way later. Screws over the tech illiterate - probably no idea where their homework went. It would be much less harmful if they were just selling them as reject/lower capacity.