Thought I'd provide some updated thinking here.

As mentioned above, I bought a bike from The Pro's Closet last year. This is a high end ti/carbon cyclocross bike. Yesterday, I noticed a crack in the weld of the rear dropout. The bike was not crashed and the crack was not there before, so it looks like a weld failure. Who knows if it's fixable. The frame builder does not offer any warranty to anyone but the original buyer, again not unreasonably. I emailed the manufacturer about the possibility of paid repair, but I haven't heard back yet.

What to do in this situation? The Pro's Closet does not offer any sort of warranty or post-sales support. It's probably unreasonable for them to do so and I don't blame them. The manufacturer is unlikely to offer anything beyond a costly repair (which is probably the road I'm headed down here). No shop around here is going to help as I didn't buy from them. Again, no one is doing anything wrong here but this is all obviously a MAJOR reason to not buy a used bike in general: you're kinda screwed if something goes wrong.