Possible front door scam

Local information from one member, confirmed, by a number of others.: 
“I thought residents would like to know that a man is going door to door claiming to sell anti-body tests.  He informed us, through an upstairs window, that he was from the Harley Street Clinic We rang the clinic, who denied all knowledge, as you’d expect.  The police have been called.”
They are smartly dressed. wearing clear plastic face visors. 
D&D