Who is liable for chargebacks?

The merchant is ultimately liable for chargebacks. The money returned to the cardholder comes from the merchant. The merchant pays any and all fees for each chargeback, and penalties are assessed against them. If a chargeback is unwarranted, the burden of proof falls on the merchant. And even if the merchant proves a chargeback was unwarranted, they get the revenue back but the chargeback still stands on their transaction record.