The photos of the Rohloff gearbox should really show either:
a) a blue and yellow plastic sticker on the box with the serial number
or
b) the serial number laser-engraved on the metal
This is quite an important matter as Rohloff factory service is conditional upon the serial number being on the gearbox, or in exceptional cases the owner otherwise proving ownership.
However, if the fellow on Ebay says this was his personal Rohloff, and he has an excellent reputation, that's probably good enough, as long as he gives you documentation for the purchase (a receipt of some kind) and a warranty document (a red card with a perforation along one edge where the Rohloff half was torn off by the dealer to send to Rohloff). The warranty isn't actually transferable but it carries the serial number and is a further indication of ownership. The seeller may not think about sending it with the gearbox, so ask. Also ask for any service history he has -- there's an annual service document that comes in the box, supposed to be stamped by an official dealer, though most of us just do the service at home with the service materials Rohloff sells.
Even if the box is long out of warranty, and the warranty is in any event not transferable, there may down the line be some advantage to you, quite apart from secure ownership and the moral obligation not to buy dodgy goods. First owners get an unofficial lifetime warranty in that Rohloff generally does not charge owners who do not abuse the box, and sometimes not second owners either. It's an ultra-reliable box so this extra effort may never be "monetized", but you never know, and you're investing quite a bit more than you would for a lesser gearbox at least in part for the security of this longevity, so it is worth putting some effort into the documentation.
Good luck!
