Thanks, y'all!
OK, then. Hopefully, it'll still be there tomorrow. Price wasn't hideous, bore is uniformly rusty, but probably usable with some work. The main downsides: replaced rear sight with single fixed leaf, extra checkering on the area between the bands that doesn't at all match the checkering in the usual spot, and somebody attempted to remove the breech plug with a pipe wrench on the barrel.
The flintlock musket I was more interested in probably is already spoken for. The drama with not being a regular customer...