Can I choose to follow-up only my purchases and not my sales via OkiOki?

Sure. If you don't want to track sales invoices in OkiOki (and therefore also not their payment status), you can specify this in the 'Settings' as follows. OkiOki will now

• ignore your sales transactions and therefore not put them on your to-do list.
• ignore your sales invoices and therefore not put them on your to-do list.

This will not stop OkiOki from picking up your sales invoices, should she find them in your linked mailbox, but they will never show up on your task list.