It is ONLY OK to retract a bid if...,

You accidentally enter a wrong bid amount (for example, you bid $99.50 instead of $9.95). If this occurs, re-enter the correct bid amount immediately.
The description of an item you have bid on has changed significantly.
You cannot reach the seller. This means that you have tried calling the seller and the seller's phone number doesn't work, or you have tried emailing the seller and it comes back undeliverable.

Thats what ebay has to say about bid retractions. Changing your mind does not qualify and according to ebay is grounds for suspension.