There are lots of 18650 "manufacturers" that actually just buy used batteries, re-wrap them, and sell them as new. I imagine that used Tesla battery packs may be used for this purpose pretty frequently. Unfortunately while this activity provides a great value for the players involved, the batteries are often passed off as new high-discharge cells to consumers who use them for vaporizers or flashlights. Using old spent cells for both of these use cases can be dangerous, but it's particularly worrying in vaporizers because the battery may fail catastrophically inches from the consumer's face.