A dozen years back I worked at a University. All of a sudden in December we'd get flooded with people trying credit cards out in rapid succession, always small

A dozen years back I worked at a University. All of a sudden in December we'd get flooded with people trying credit cards out in rapid succession, always small amounts of a dollar or more. What's worse is that sometimes alumni couldn't even get access to the site to make legitimate donations. The charges that made it through were always reversed. Sometimes they even fined the university and they were viewed as the enemy. It was a royal PITA. So they did two things: Blocked certain IP blocks from Eastern Europe and declined all cards if the amounts were small. I didn't code it personally, just learned about the problem and solution in a meeting.