When you stray from established, well known sellers it's a crap shoot.
Of course this is no guarantee that it will not be revoked in the future - I've only known of this happening once however (out of a couple dozen at least). 99% of the time if you buy from a seller with a good number of positive reviews - the key works. How can one know if they are pirated and/or bogus.
There is a difference in selling/buying legitimate licenses, if allowed in your area, and entirely pirated/bogus keys which may be what you are getting.
