Affiliate mark a sale as paid in cash

Don't know where this fits in so opened a new topic.

We use affiliates (with friendly URL) to sell and sometimes its a direct sale where the affiliate has the product (mobile phone SIM CARDS) in hands and is with the new client and receives payment in cash.

How can I make it so that the actual affiliate who sold the SIM card and received the money can mark that sale as "paid in cash"?

When he sells and payment is in credit card this is automatic, but how can I make it so that when he sells in cash he has some sort of administrative right over that specific sale to inform that he has the cash and he will be the one responsible for that specific amount?

Its not a problem that he keep the money because the 1st payment is his comission so actually informing that we received the money is not a problem

Thanks
Marcio