Velocity limits or velocity caps are a good way to prevent abuse and fraud.
The transaction velocity in Rebilly is defined as the number of transactions of type authorize, capture or sale from the same customer within the past 24 hour period. As time goes by, the velocity will change.
The following video demonstrates how to temporarily blacklist an abusive customer.
Instead of temporarily blacklisting (which we also refer to as graylisting) you may permanently blacklist or use the "increment risk score" action to influence a risk score that you calculate.