I have asked a lot of people about this problem and no one seems to have a clue. I'll try to explain this so it makes sense...here goes!
I help with the web design of a website called http://www.playworshipguitar.com. We had gotten on the first page of google for most of our keywords then one day I noticed that our exact spot on every search engine result page had been replaced with an affiliates link. Our Title tags and descriptions remained the exact same but the link is now going through this person's affiliate link so they are getting credited with every natural result sale we make. We use Clickbank as our merchant solution and they said the problem was not on their end.
I also contacted our hosting company and they said it was nothing to do with the hosting. So all I can figure it that it is a wordpress security issue.
I have noticed that if I make a change on a page and it is re-indexed by google that sometimes the result will return to our own link. But eventually it will end up switching back to this affiliate's link.
Anyone have any clue what is going on here?