I think it depends on which products you promote and how you promote them. Fitnfree is right as there are quite a bit of refunds but I've learned to minimize those by actually buying the products myself and doing a personal review so my audience knows exactly what I'm getting. I hardly get refunds now.
If you are going to sell any kind of product, whether it's from ClickBank, CJ, LinkShare, etc. you have to understand the art of PREselling. In other words, you must warm up your visitors with your own good content first and then make your visitors want to buy.
So many affiliates focus so much on the products before really establishing good content on their own sites that will help improve their affiliate sales.
Now some people are savvy with PPC and they can take Clickbank products and make products from AdWords, etc. but I was never good at that so I prefer to take the slower approach. But it works well.
