The study was specifically careful to make the wallet appear to have been lost by a member of the local community. Returning the wallet is an act of civic honesty as it relates to helping someone who is essentially a member of the same community, someone arguably bound by the same social contract as the person given the "lost" wallet.

Interesting. Last time I returned a lost wallet, it was to New Jersey (I'm on Canada's West coast, where this was found). People will return wallets from outside of their community. It seems odd to restrict them that way and then ascribe the motivation to some "civic" reasoning.

I'm guessing that's because they measured the return rate of institutions:

"Wallets were returned to one of five societal institu- tions: (i) banks, (ii) theaters, museums, or other cultural establishments, (iii) post offices, (iv) hotels, and (v) police stations, courts of law, or other public offices."