I think on the surface that sounds like a great trade for you. However, I would be concerned why he wants to trade. No offense but a 3.0 isn't nearly as desirable as a 4.6 and the fact he's throwing $6k into the deal seems almost crazy. I would think straight across or even asking you for cash would be what most would consider reasonable. I'd be wary of serious potential flaws with the 4.6 with that sort of a deal, but if it checks out, take it and run! (oh and either paint the centers of the wheels black or gunmetal or put 87s on!)

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2001 X5 4.4i
2002 Honda S2000