You have sinned. More minis than you need? Blasphemy!
I don't play at FLGS but I think it's ok to charge, it's not that different from paying for a couple of hours of snooker or bowling.
OTOH being paid to DM doesn't convince me. I am usually the DM, and if they paid me 20e it would mean nothing to me, but if they offered me some serious money I would probably take it very seriously. The problem would be then, if it would start to feel like a job instead of fun. But to their merit, they say in the OP that the DM doesn't earn cash but store credit ... getting a free book or set of dice for DMing would have an entirely different (good) feel!

Even "free" home games aren't free. Unless you freeload.
I kinda love the idea of "cheating for charity" at public D&D events. Socially conscious and funny at the same time!There's a system of reroll tickets (say 5 for $10) at some of our local games, ostensibly for charity but extending into our normal games as well. I understand it being tolerated for special events but it's not something I want to insinuate itself as common practice in general public play.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.