For me, it really isn't worth even considering anymore. I have only command control engines and haven't had the best experiences in the used market. For another $100-$200 more (give or take) I would much rather have a new item with a full warranty that you know has not been abused. Rolling stock may be of slightly more interest, but I no longer go looking for anything used.
Edit: After seeing Marty's post above, I would consider something used that Marty F, GRJ, GGG and maybe some others here had thoroughly gone through and repaired. I trust their work, they are very reputable repair folks. I think this would as good as purchasing a new item.