I can't speak for the other questions you have about the service being offered, but a Chargeback is when a customer has completed a purchase; found the product/service not to be what he expected; has attempted to return it or resolve it with the vendor (you) and is left with no other choice but to call his/her bank and contest the charge.
Typically, the bank will get the charge reversed so the customer gets his money back. The funds are AUTOMATICALLY removed from YOUR account plus (usually) pretty stiff fees for chargebacks.
Basically, if the client had to go this route, you're not following a very good 'customer service' procedure. Ulitimately, they have tried to get their money back, and couldn't. So they generate the chargeback.
Hope this helps!