People call and say they want their money back.

In 2016 some campaigns got in trouble for turning one time donations into monthly ones in the fine print.

They give refunds when illegal campaign contributions become public. Usually with a mea culpa that "we accepted (these contributions clearly in excess of legal limits) by mistake". "We have returned the contributions so as to not violate any campaign finance rules, which we always follow."

That's an interesting stat and a good one