likely what they are implying is that chargebacks have indirect costs that you can ballpark around $50 per chargeback. So steam would likely take back the $5 revenue from the developer for the $5 chargeback, but the costs of processing the chargeback are absorbed by steam. i do not know if they have a separate chargeback fee they charge developers for it but it wouldnt make sense to as steam is the one validating and processing payments