What are red flags on a survey?

A low response rate is the obvious one, but also watch for a lot of incomplete responses, suspiciously fast completion times, and answers that are identical or contradict each other. Any of these can mean the survey is too long, confusing, poorly targeted, or being clicked through without much thought. Leading language, emotionally loaded wording, and answer choices that leave out reasonable options are all warning signs too.

If your sample is just whoever was easiest to reach, you're probably looking at selection bias - check how different your respondents are from your actual customer base. Red flags show up after the survey as well: feedback nobody reviews, or questions asked without a real purpose behind them. A survey should lead somewhere. If it's just producing a spreadsheet nobody opens, something's wrong.