Interesting matrix!Warning! I'm probably going to bore you to death but rest assured that I do these kind of things to help not aggravate. I've included a file that shows a simple decision matrix on evaluating a used tractor complete with an example. Just bear in mind that so much goes into making a buying decision that the only way the value point is finally set is when you are loading it on the trailer.
The devil makes us engineers do things like this.