First off, do some searching. That's been said. But I HATE guys who just say that, so I'll add my .02

Love the diesel X5. Lots of power, handles well, drive is what you'd expect with a BMW. It's not perfect, but I feel like that's more around what the EPA has forced on these guys and NOT a BMW thing. The only issues we've had have been diesel emissions related, you'll find threads about the faulty DEF tanks--get a clean CPO one and if it has issues they'll fix it, give you a loaner...not the end of the world.

We have two boxers and the grate thing that goes across the back--they love the car and it fits them fine. If you have larger dogs (they're about 65lbs each) you'd maybe want larger but that's up to you. Great room either way.

Get one highly optioned. We did and I'm glad we did. The options are a ton more new...but lose their value quickly used. We have every option but the rear DVD screen and it's nice stuff.

If you do get a diesel, learn how to do some 'handy' stuff yourself. Like when the DEF needed filled I learned I can go to the truck stop and pump it right out of the truck stop DEF pump into the two tanks with zero issues and it costs $2.50 a gallon instead of the robbery BMW wants to charge you. Use a local shop for oil changes or if you're CPO plus the extended maintenance do that (obviously). Overall I'm very happy with the car and to date we haven't had any real issues, just funny check engine light stuff that the dealer fixed. All new part numbers and *knock on wood* they got the bugs worked out.

I've heard they're extending the warranty on the emissions related stuff as well--EPA is obviously the 800lb gorilla here and a faulty DEF tank won't fly at any mileage. If it's required for the emissions to operate I've been told the EPA is talking 12 years unlimited mileage on all diesels and all manufacturers. We will see, but I think at the end of the day the emissions issues will be on BMW's shoulders like they are on VW etc.

You're in a neat spot here--I'd for sure sell the car back as that's obviously a good deal. I saw a news report of scammers trying to buy cars (and dealers) on trade way low knowing they can get the full buyback $. I'd either make the dealer take it to the penny for the buyback or give it back. Then go drive everything used in your price range, lots of great mid-size suv options out there. We did the same and settled on the X5 but I'm in Denver and have a ski house so travel during the winter was a top priority.