The explanation for not accepting 500 eur notes when you generally sell stuff for <100 euros is that you're asserting that your cash drawers won't have 400+eur

The explanation for not accepting 500 eur notes when you generally sell stuff for <100 euros is that you're asserting that your cash drawers won't have 400+eur in cash so you can't ever give out change from a 500. However, if you're making a jewelry purchase with multiple 50 quid notes, denying them would seem unreasonable.