The main character will quit just as soon as she figures out how to sell the gold without drawing unwanted attention. It's not that she would mind paying taxes, it's just the whole "being in jail for felony theft because she can't explain where she got it from" that palls.

She managed to get enough scrapings off one to cover the next year or so of Steve's lattes, so at least she's not out of pocket anymore.

But aside from...shall we say "mortal" concerns? Aside from those are the supernatural concerns. Shortly after she worked out just how much Steve was tipping, she saw that Tumblr thread about Fey running a coffee shop and the dangers of not paying fair value.

Could accepting an extreme over payment count as a deal with a demon? A few days of reading and she added "may be given of your own will and do not bind us together by any contract" after "TIPS" on the counter jar^* . She's taking Steve's lack of reaction to the change as a good sign. But she's also not rushing to get that gold sold.

^* Actually a brilliant move, tips from human^& customers tripled after that

^& At least she assumes, hopes, they're human