Good question: I think CB product selection's probably the single area where most affiliates make mistakes that are most expensive in terms of opportunity-cost.
Here's my own 10-point checklist for CB product-selection (and these are more or less the order in which I look at them, too, I think):-
1. Has to be a niche in which the prospective customers are not already Clickbank affiliates themselves (obviously! - otherwise how can you possibly ever earn an affiliate commission on a sale to them?!) - so for me that completely excludes the "IM advice" and "make money online" niches.
2. No leaks on the sales page: (no opt-in, no "free trial", no "contact the vendor here" etc.)
3. No ridiculous hype or deceptive tactics on the sales page (nothing obviously non-FTC-compliant, no phony urgency/scarcity, nothing clearly deceptive/dishonest, no credibility-losing claims, no income-claims, no cancer-curing claims, no deceptive crap about "as seen on Yahoo/MSN" which people will rightly ridicule!).
4. No pop-ups/discounts.
5. Gravity not too high (over 30 puts me off a bit; over 60 puts me off a bit more; over 100 I won't consider at the moment).
6. Sales-page looks to me as if it will convert my traffic well (obviously subjective and not entirely reliable, but as a copywriter I like to think I can guess pretty well, and I can tell whether it's "professional copy" or "home-made copy" - and I don't care about anyone else's traffic so "overall conversion rates" aren't relevant to me, not that they're available anyway).
7. Good product (I don't promote anything without seeing and assessing it myself, obviously)
8. Good vendor reputation/attitude/behaviour (I'll contact them first, one way or another, and if I don't get a reply I won't promote their product, because I can imagine what their after-sales behaviour will be like if they won't even reply to a prospective business associate).
9. Reasonably high earnings per sale (75% of small amount, 60% of medium amount, 50% of larger amount etc.) - I slightly prefer more expensive products around $100 when I can find them, because I think they're easier for me to sell than cheaper ones (really).
10. Has to be something I can write about (I'm an article marketer) - for me, that probably excludes anything terribly technical or for which I'll have to go to night school to understand the vocabulary.
The things I don't really care about, though I recognise that some affiliates do, which are therefore not on my list at all, are (i) "% rfd", and (ii) affiliate gimmicks (banners/articles etc) offered by the vendor, which I'm probably not going to use anyway. I strongly suspect that almost no professional affiliate has much interest in "marketing tools" provided by the vendor or really takes this into account in product-selection.
In my first 4 or 5 months as a Clickbank affiliate, I earned very, very little. The two things that made a huge and dramatic difference to my income were (a) not touching anything with a vendor's opt-in on the sales-page, and (b) staying well away from high gravity products. I changed just those two things and quite quickly I was really making a living, and have been ever since.
