Even worse was illegal software. There were 720KB (Double Density) and 1440KB (High Density) 3.5" diskettes (amongst other sizes). The disk drive would detect the difference by an extra hole in the disk.
People would buy cheaper double density disks, drill a hole in it, so that the same diskette could be used as a 1440KB disk. Of course, they were of a far lower quality, and 'arj' (which was popular at the time) would often fail after the n-th disk.
I used an Xacto knife to create an extra notch in Commodore 64 5.25" disks back in the day so that I could take the single-sided disks and make them double-sided.
I would take one disk flipped over the other, mark the notch with a permanent marker, then cut out the outline. Most disks, like Elephant Memory, would work fine. You just flipped the disk over and inserted back into the 1541 to read the reverse side.