I highly recommend that for your first set of questions you either use filter surveys (ask for age, location, gender, etc) to target people who are in your target user demographic, or have test questions to make sure they really understood your pitch (ex: Summarize this product in 30 words or less).

In my studies, I limited the respondents to the US, because I was getting too much noise from international workers. I also gave them the option of leaving more detailed feedback. Most of them did, to my surprise.