This is the problem with Pay Per Post. There are no guarantees for the blogger/publisher. The ball is all in the advertiser’s court and if they make a mistake it is the blogger who has to pay with his/her time/ideas.
I’ve made a few dollars with this blog over the last couple of weeks using Pay Per Post sites because I wanted to check out the way that things worked.
At payperpost.com you complete a list of the sites that you wish to register to be considered for Pay Per Post by advertisers. Blogs/websites with a page rank of 2 upwards seem to get the most interest and the better monetary rates.