To see pictures of what you should be seeing with candled eggs at various points in development, check out BYC's "Learning Center" at the top of every page. Then go to the first topic "How To" and click on "Candling eggs" which is underlined. This helped me a lot.
I had some disappointments with shipped eggs too. They were from good reputable breeders, but the shaking/jostling/dropping that the post office does, simply isn't good for them and some don't survive that. The biggest help candling was to me is that the clear unfertilized ones could be discarded early on and then I could focus on the ones that had a chance.
By the way, I had almost given up on my eggs at day 22, but didn't have the heart to toss them yet. Good thing, because 3 more hatched on day 23-24! Yes, I counted carefully, but they just were on their own time clocks (Probably "Island time").