I kid you not but one of our customers told us that someone from Microsoft rang him, connected remotely to his computer run some checks/scans/fixes and then persuaded him to purchase some sort of unlimited technical protection for the whole year for like £70.
The funniest thing was that he actually believed that his computer was running better/faster after that.
We obviously told him that he was most likely being scammed and sent him few links about those sort of scams, told him to contact his bank and get his card changed/monitored, we also told him that they might have installed some malicious software on his computer as well.