I agree with Bodercollie. As far as a 3 to 5 year old rig from a private party. That is what we did. Worked out great.
One issue you may run into though, many folks bought new at an inflated price, they are under water on the thing. Can be difficult to find one at say a low NADA book price, ( which is what I look for as a buyer , with no options added in by the way) So can be difficult at times to find a private party that will sell at that price.
Takes a while for them to get used to the idea, that just becuase they owe XXX does not mean the rig is worth XXX