I think there are actually a few places in the world where the custom is to do the work and then get paid afterwards, with complete trust and knowing the buyer will do that.
Some genuine Japanese restaurants have, or at one time had, the custom of bringing huge amounts of food to a table without having first presented any menu with prices, and continuing to heap food on the table until being begged three times to stop, then never presenting a check. The patron would leave an amount they felt appropriate. I experienced this in a remote part of Hawaii.
There is another country I can think of with similar customs. It is possible this is the first time sellers have encountered the idea of paying for anything first.