I'm sorry you're displeased, but it is a used car you bought from a dealer. To expect them to know the details of the cars history is a bad bet. It could be that the story he gave you is what the PO told when they traded it in. Really in my opinion his mistake was saying anything beyond "all we know is what the carfax says".
I have no affiliation with that dealership and haven't been a customer. I'm just pointing out that based on what you posted, you didn't really get screwed since it sounds like you had all the information before hand.
I personally would have wanted it examined by an independent shop with an accident showing on it's report (which means I wouldn't have bought it since dealers don't like that).