Come on, man.

Remember those guys last year who would drive around buying up all the masks, selling them online for 10x? You don't know why everybody hated them? This is why:

The original seller has a reputation to protect and doesn't want to be seen as taking advantage. Maybe it's a musician who would rather sell to kids who are willing to wait in line than to whoever has the most money. Maybe a pharmacy selling masks in 2020. The arbitrage opportunity is for somebody with no reputation or scruples, who chooses to see themselves as just an Angel of the Free Market. To everyone else, he's a jerk.