Here's an example, although not a good one from Craigslist.
There are numerous ways to do reduce fraud, abuse, and increase compliance. Trying to get stats on all or most of them will be very difficult. Especially because many companies that use systems to reduce fraud either did it from the beginning or won't release numbers because of data security and risk of a back-lash for the numbers being worse that the public though.
If you are trying to find a solution for a specific case, the best bet is to go through all of your options and logic out which one deters the most fraudulent people for the best cost and implement that option or set of options.
I will say from experience that no system is going to be 100%. We used Lexis Nexis and 2 factor authentication at my previous job and we still had a handful of fraud case a month.
Finally, there is a difference between reducing illegitimate use of your system such as what Craigslist did and decreasing cases of fraud. Specifically, fraud is usually always low in volume but once people find a weakness in your system they will attack it repeatedly. Whereas Craigslist had an issue with people abusing the system in a way that wasn't necessarily illegal in itself but was looked on poorly by the general public.