Rocky, all of the Tesla Model S PB calipers I've seen on eBay have been taken from wrecked Tesla's. There seems to be a lot of them! The calipers that were exchanged under warranty were supposed to have been destroyed by the servicing dealer. Imagine the liability risk a dealer would suffer if they were taking those "exchanged under recall" calipers and selling them on eBay! That being said, only 5% of them were defective, so if some found their way onto eBay, chances are they're OK. I agree with you; the challenge, buying them on eBay is, receiving undamaged units. The electrical connector is extremely vulnerable and even if it is intact before shipping, if the packaging isn't great, the calipers will be delivered with broken connectors.
I bought a pair of the later composite PB calipers on eBay for $75 each and they look like brand new units. They came with pads too! I went this route for one simple reason; it allowed me to eliminate the e-brake handle and move my Recaro passenger seat a few inches closer to the console.