It arrived! My 2nd Tandy 1000SX got here today, but the sound I heard when I took delivery was a bit ominous. It sounded like something rattling around inside. So I got it unpacked and opened it up. First, the case is a bit worse for wear. There is considerable rust on the chassis, and the plastic is a bit scuffed and has a couple of small cracks. Also, two of the slots don't have covers, but there is clearly a modem in the eBay picks. So once the case is open, I discover the Tandy 1200bps modem lying inside, but also some sort of hard card lying loose as well. The hard drive is likely dead after banging around, but it was completely unexpected. Also, one of the ROM chips is a lot higher off the motherboard than in my other 1000SX, so it's likely there is a smartclock in this one, so there's that. Once everything was back together, I hooked up my monitor and keyboard and... 640K appears on screen, the 5.25" floppy seeks, the 3.5" floppy seeks, and "Non system disk or disk error" eventually appears. I put in my Tandy DOS disk and press ENTER, and it seeks the 5.25" drive again, but fails to boot. I am uncertain whether it is the drive or the disk (I suspect the drive, as I believe I previously tested the disk in the other Tandy) but my troubleshooting stopped there, for now.
Some thoughts on this system: despite not getting a DOS prompt yet (and even if I don't), I'm happy with this purchase. It works well enough to make a good backup to the other one, and the RTC and 3.5" floppy can be moved straight over to it for immediate use. It would be awesome if I could get the hard card going, but it's no loss if I can't. If I can get to a DOS prompt, then I'll likely restore this one too, but if not, the parts I'm definitely using are more than worth what I paid. :)