market researcher versus telemarketer

I find that Market Researcher's have a valid purpose to ask if they can ask ten minutes worth of questions. The telemarketer is always selling something. It is very invasive to call my home to solicit their service or product when I have had no previous association with them and can't stand it. Since I find that we get these calls at the most inconvenient times, it is annoying to say the least. I am far more inclined to take ten minutes to answer a market researcher's questions than listen to a telemarketers speal. I have found some to be very rude, whereas the market researches have always been very polite, which makes me more inclined to help them out. All in all, I rather not receive any calls of these kind. It really bothers me that they have my number and call in the first place.