One of the study authors here.

On targeting front-desk employees, we did this both to allow relatively portable cross-country comparisons and for reasons of internal validity (e.g., if we placed wallets on the ground, then can participants "select" into the study which compromises our ability to draw causal inferences).

On your last point about whether it's dishonest to hold onto a wallet. The question is about the treatment effect --- all things equal, is it more dishonest to hold onto a wallet with money vs no money? We polled nationally representative samples in the US, UK, and Poland and in all three countries most people thought so.

Amazing study, was really interesting to read. How do you get to do this studies? How does someone get into social science like this? How did you pay for all the tickets for all the cities?

They said in their study that even when they accounted for GDP, the effect remained.

I was thinking of Gini coefficient.

Are there any ancient moral traditions that espouse 'finders keepers losers weepers'?