 I bought my "Certified" used Explorer Sport in 2005 and have had nothing but problems with it. 1 month after I bought it, the ignition lock tumbler locked in place and I couldn't even start the car, and my key was lodged in there.  Ford charged $300+ to fix it.  Then, the center armrest completely broke off after leaned on it just a little bit to get something out of the back. Third, the 'check engine' light will come on for the smallest reason and stay on. Then, my drivers side door will not unlock from the outside, it will only unlock from the inside.  So getting into the car requires using the passenger side door to open the drivers side.  I've only had it for 1.5 years!