we can trust only your "words" because some one buy a key and left a feedback in a limited time period, next he try the license.
If these key are not legit there is even the risk they could be blocked.
If are legit ok, you are good samaritan and you sell for an awesome price! Yes did it! Thank you from all!
But this single key, if I remember could be taken officially from market and windows not sell it.... mmmmm
good business!