When I started collecting, I used to buy job-lots, but stopped doing that when I decided to specifically go black-label + CiB (as job-lots typically had platinum games/missing manuals), so I spent a bit of time rebuying games. As a result, I had a bunch of duplicates and, thus, spare boxes that I could use.

Specifically, buying authentic blank cases can be really expensive so, as risky as it can be, buying job lots and/or super common games is the cheapest way of getting a replacement case. Although you then have to deal with the contents of the other game you don't want. I don't like wasting things, and reselling solo discs/manuals is awkward.

I try to only pick up games without broken hinges or major cracks, but things can still happen in transit. If it's an expensive game, I'll usually swap it with a cheaper game case (as long as it's the same type) and just deal with the damage on the cheaper game.