Given their are few materials to actually buy as you already have the charger, payment after completion is the only reasonable option.
I’d have thought the cable and pen fault device will be on trade credit from the wholesaler. The rest of the cost is small sundries and labour.
I’d not be paying for that work upfront, particularly if they want bank transfer. Zero comeback on that if they ghost you. If they wanted it upfront, they’d need to accept credit card and eat the fees themselves.