Vicky asks walt, a cobbler, to repair a pair of boots. there is no discussion of a price, and vicky and walt do not sign any documents. after the repair, walt hands vicky a bill. with respect to vicky's obligation to pay the bill, this is

I would say that Vicki and Walt have a business relationship based on trust by Vicki that Walt will not charge too much and by Walt that Vicki can pay what he asks. To eliminate doubt, it is best to confirm the charges ahead of time and thus have a relationship as they say in Latinamerica, cuentas claras amistades largas or in other words clear accounts and long friendships.