Hmmmm. That is a tough one. I agree with HiFiHoney. Keep your mouth shut. It is not your job to educate the consumer post purchase. In this day and age, with the power of googling and the internet to research just about anything you'd care to buy..........if someone bought the divinchi speakers and seems pleased with the purchase, so be it.

I am a small contractor. Part of my job is selling the work. Often in people's homes they will proudly show me remodelling or painting work they have done and basically say, "Gee, doesn't that look Great!" As often as not it looks amaturish, and badly done. Is it my job to educate them to just how clumsy their work looks? No, it isn't, unless it will directly affect the work I am being asked to look at, then
it is my job to point out how their mistakes will affect my work.
In your case, does the fact that they purchased crappy speakers affect you or your ability to sell them electronics?
Now, if they ask for your honest opinion on their purchase, then you can use your expertise to educate them as to what makes a good speaker good, and a bad speaker bad....