It costs the Lexus dealer ~$1800 to have a car certified, they have to pay that to corporate as an extended warranty, since you can take the car to any Lexus dealer for covered repairs. So they pass this along to the buyer to cover the cost. The inspection for certified is very thorough, and anything they find gets fixed /replaced before the car can be sold. If there are any accidents on the Carfax it can't be certified.
We bought a certified IS 250C convertible this spring. It wasn't cheap but I wanted coverage on that insanely complicated retracting roof. They put new Michelin Pilots and all new brakes on it before it went out on the lot.
If you find a truck you really like but it's not certified, get an extended warranty.