What are the criteria that one would need to fulfill to be able to participate in like 99% of the advertisers' campaigns? For example, I run one blog that's about long distance calls, and Rebtel accepted me instantly (and today got my first commission, $25, woohoo!), but Skype declined me. I sent them email asking about this, but so far no response. I'm not exactly advertising Skype on my site as of now, just listing it as one of the best VoIP-programs, but I'm sure I'd get some sales as I already bring them some occasional traffic.
Mind you, this blog is like three weeks old, so I'm still mainly on the second SERPage for my keywords, and thus not getting that much of traffic (15-20 UV a day - and these are mainly from one local blog directory).
I have other, highly relevant blogs with 100% unique content (for the niches I've tried to get into), with much more traffic, but mainly the instant decline rate has been 99-100%. I always choose only the advertisers for the country I'm targeting, but why is the decline rate so high?