I was wondering how many people buy the product before they become an affiliate? People say that the role of an affiliate is to pre-sell the product, eg. talk about how the product has benefited you and convince them that they need it too. This means that you need a pretty good understanding of the product which you can only get by using it yourself.
I almost always buy or trial the product and test it before promoting it. Unless it's a situation where I get a free product to use because they're hoping I'll promote it in return. You can definitely pre-sell a product without buying it first if you prefer, as long as you understand the market for the product.