When Sponsors Don't Follow Through on Paid Posts

Like many of you, I like to blog about whatever is going on in my part of the world as well as accept material from other parties for my blog from time to time.  However, I only accept content from third parties when I approve of the subject matter and I also write original content for them when I feel the topic suits my blog and would be of interest to you.

Having said that, up until now, I've not had a single sponsor refuse to pay me once I honor the terms of our agreement and publish the material as outlined.  But recently, I've had to remove a post consisting of entirely original material written by me because the third party refused to make payment.  The excuse  for nonpayment was "google was not indexing all my blog pages"(or something equally as lame).

So I guess what I'm wondering is if any of you have had a sponsor refuse to pay you after the fact and if so, what did you do about it?  If you haven't run into a situation like this yet, what would you do?  Is there a list or blogger out here who is collecting information on this for us?  I really appreciate any info or advice.