The merchant should accept a chargeback when:

the transaction is known to be fraudulent;
the evidence is not compelling enough;
the chargeback amount doesn’t compensate the effort to gather compelling evidence;
the merchant failed to refund the customer before the chargeback date.

The merchant should dispute a chargeback when:

there is strong evidence to support the case;
the chargeback amount is significant.

Disputes that involve transactions already refunded before the chargeback was created will be automatically disputed by PPRO on behalf of the merchant.