I was going through a few programs today and noticed that almost all of them don't have a feature I would think is basic and standard:
A "Payment History" page.
Why wouldn't you have this? It's very easy to have and I think affiliates find it very useful to see when payments were sent out by what method, for what amount and covering what period.
I just assumed everyone had one until today. Strange.
Anyhow my free advice for the day is to programs who don't, implement one soon. Your affiliates will probably thank you and it can only build trust.
