Please help! Thank you!

[swisstype]

I am on the verge of buying a 2008 BMW X5. It is a CPO, was bought at the local BMW delaer, same as where it is now, they have the service record, which is squeaky clean, a carfax, and was traded in by a loyal customer for a new 7 Series. It has 15k miles, and is loaded. The only things it does NOT Have are the Sport pkg and the M sport pkg. It has the rest. It has std tires and wheels, but this is a really clean auto. I had it put up on the lift, and really went through the thing. I am considering trading my car in, and was wondering what you all thought was fair as a main price. They are at $55k. I can justify this as they are giving me absolute top $ for my trade in, which is pristine as well, and I am not losing out, as I see me stepping into something much better. Please let me know what you all think, if there are things I should look for, things I should be careful of, and hopefully, I will be a regular member here! Thanks so much!