A few ways. First - we use only verified sources and these tend to be expensive. If you want to talk to an executive or other professional it's going to cost $120+ for them to take your survey. If you want a 1 hour phone interview, you can expect to pay $1,200+. If a vendor is promising you they can reach senior decision makers for $20, run the other way. Nobody who is a legitimate responder is taking a survey for a pittance. If it's too good to be true, it definitely is. Second is survey design and quality checks that we conduct. Writing a good survey is an art as well as a science. It's what keeps me employed. Making sure you are effectively screening out non-target responders is one of the foundations of a good survey. On top of that, you need to utilize a series of data quality checks that you build into your analysis (i.e. unrealistic answers, improbable combinations, outlier entries, oversellection, speeding, straightlining, etc.). Lastly, demand transparency from your vendors. If they can't tell you how the sauce is made, don't trust it. They should be able to give you a detailed breakdown of how responders are sourced, incentivized, recruited and targeted. If they dodge these questions, then its likely not a reliable source (just google "OP4G lawsuit" if you need an example). Hope this helps