This was in my area and I thiink would have been a pretty good buy in the low 20s compared to auction sites, espeically for the Northeast where most rigs are pretty rusty and this is pretty decent and would save someone in the northeast a bit on shipping and the opportunity to see in person. Looks like it's sold now so hopefully a Mudder got it and was happy with the deal.
To the OP, if you're looking for a low rust 06/07 ~140k miles for $18k I don't think that's going to happen unless you get lucky and are willing to buy sight unseen over FB marketplace/Craiglist in a low rust area. Good luck with the search.