When this usually happens, I see it as a chance to practice my Korean...or embark on a super-sonic speed dating session if you will. Regardless of what sales pitch they throw, I ask them "What's your hobby?" or "What do you think about tofu stew?". After doing this for 2 years, I realize men and women in Korea would pound that red buzzer and dunk me into a vat of sticky rejection...which I'm OK with. I do the same thing in the States when tele-marketers called. To answer your Q, it happens often and capitalism never discriminates.
Also, if you're not interested, K salespeople hang up faster when from the other end they hear "I'm not Korean/외국입니다"