The decision for the blacklist was a MM decision with GMod approval.
Furthermore, this is not only looking into a single report but over your history.
The blacklist system is in place to prevent previous "scammers" (note quotation since I'm not claiming everyone who "scammed" is a scammer, but rather couldn't respond in time) from coming back in and doing it again.
3 months blacklist isn't much.
Original blacklist was because you failed to refund $50 for two customers with a wait time of a few months.
This is an additional few months of $78