Certified? So I am assuming you are looking at USED SUTs. You know they are offering the 0% nowadays and unless you are paying cash, I think you are better off with a brand spankin' new H2. The Hummer dealers need to get rid of the 07s because the redesigned (sort of) 2008 is around the corner. Also, others have suggested buying from a different State if the savings are substantial. Try SoCal
If you are set on the used SUT, make sure you get a CARFAX report.