My girlfriend is a "camgirl", and this behavior reminds me of the behavior of the lower tier, more shady cam / phone-sex sites.

The bigger sites that take a large percentage of the customer's money (40-50% goes to the site, not the model) also protect the models from chargebacks. Sites that take a lower percentage do not. One site she worked for ("cam model directory") has a spreadsheet of customers who are known to issue chargebacks that the models have to monitor before taking payment.