Most interesting - the $13/$100 difference.
Notice that in the US and UK, the 'return rate' goes way up when there's $100 in the wallet, but when only $13 it's quite low.
In Switzerland and Sweden, it's high even for $13.
I think there might be a difference between 'core conscientiousness' and 'meaningful conscientiousness'.
In Sweden and Switzerland, it's a matter of propriety to 'return the wallet'. It's appropriate behaviour. They have smaller, tighter communities, you may even know the person. So they 'just do the right thing' because it doesn't matter what's in the wallet.
In the US/UK culture the thinking might be $13 - nobody is care, it's not worth the hassle to report. But as soon as there's money, then it becomes a material matter of conscientiousness, i.e. 'people will miss $100, it's worth the effort to report it'.
I think $13 is just not really enough money, not that much different from $0. It's almost change.
$100 is a nice, meaningful threshold.
Finally, China ... ouch.
Also, the results are perfectly correlated with transparency international index [1]
It's interesting because it may be that 'corruption' is not just a systematic issue in governance, but it may be correlated or predicted with even more basic levels of civic conscientiousness, as measured by tests such as this.