You'd have repeat customers if you charged a 5-8% premium.

I think selling Bitcoin for $85K is going to leave you with a whole heap of shitty fiat. I only need a couple of stacking customers to satisfy my fiat needs.

They're not going to spend it, they'll save it. You'd do the same in their position.

What you'd want to do is offer to buy it from stall holders at spot. Give them a Bitcoin accepted here sign.

I understand your motivation but most people won't trust you if they can't see how you benefit. The precious metals guy at my market charges a premium and buys from people below spot.