I wouldn't trust a site that talks about getting traffic, SEO and boosting your rankings if they have a PR 0... but an affiliate marketing site? hmm I dunno...
They're giving tips on how to market others products, maybe even their own, and a lot of people hide their affiliate pages from search engines so that not everyone can sign up.
They're not really teaching you about how to boost your PR, so the proof you're looking for should be something along the lines of how many affiliate sales they've made.
But it could just be a new site... or they really do suck.