Worried about buying Domain certification

Few days ago i got an email , one buyer was interested to buy my site though he found my mail address form who is. Now these client ask for me a buy domain certification and appraisal form these site http://authorize-one.net . without domain certification he will not buy my domain. So far i think and feel this site was not looking legit & they only accept bitcoin method. I was worried buy domain certification form these company or not. is is scam or legit site .

If anyone have…

Worried about buying Domain certification