- Where exactly shows it what exactly? I doubt if Windows disc manager says "1.8+ TB".
- What happens if you copy 1.1 TB of data to it? Can you copy them all back?
- What did you pay for it? In the EU it's euro 499.
- What does the seller say when you ask him this same question?

Anyway, better sell expensive things like that from a reputable shop than from 'some person'. Do you know how to get your money back if something is wrong with it?