Never got such a call either and would only accept it if it was from the shop where I bought my system, since those are the only ones who know my details.
Even then... only if they are asking you to bring it in for personal service.
Remote Assistance may sound like a good idea but in reality it's one of he biggest security holes in Windows. Once in charge of your mouse and keyboard remote users can do
anything and you can't stop them, short of shutting down the computer. In a world filled with stupid ideas... RAssist should be considered a truly stupid idea, right up there with Automatic Updates, Backgroud Intelligent Transfers and Cloud Computing.
The reduction in common sense makes such bad behavior possible as already pointed out.
In some cases they are just overwhelmed by that call or in a hurry and allow things they wouldn't allow when thinking twice.
While I do agree with both Ralf and you --Common Sense along with "La Politess Meme" is dead and buried for most people-- we do have to be very careful not to descend into victim bashing which is the prime strategy of defense attourneys and other bullies.
That said, some people do leave me wondering... Exactly how silly is it to give a total stranger unfettered access to your computer?
As one of my friends put it: "My god man are you addled? My wedding pictures are in there!" ... I'm thinking most people have no clue what they could lose...
The world is in a rush, so you have to take a break, step back and look what you are really dealing with.
I did... I finally sent an email to all my previous customers advising them of the problem, suggesting they make an appointment with my replacement to let him check their systems. Beyond that, there's not much I can do...