I'm looking at Clickbank for affiliate offers for my funnels. The criticism I hear about CB is scammy products and high refund rates.
I think I will avoid niches where the market is aware of file sharing, affiliate marketing and easy refunds.
So no "make money online" digital products that the buyer can refund after he downloads the product.
In that niche I would look at something like the "Long Tail Pro" keyword tool. It has a good reputation, is recurring income and cannot be kept/used if refunded because the software needs a license to work.
I took a quick look at some language programs they offer but I haven't dug deep enough to see if they are good.
Looking around, I was surprised at the variety of products at CB.