I am recently conducting an interview-based research study that provides each participant a $25 gift card as an incentive. The interview is supposed to be 30 to 40 minutes. I put a survey-based recruitment message on LinkedIn and received hundreds of responses. Around one-third of the responses indicated that they were interested in the interview. I contacted one of them and did the interview. However, the participant did not give me much meaningful information. The entire interview was around 16 minutes, and he could not provide any specific example on our topic. All so-called examples were very general. This alerted me that (1) he might just come for the gift card and (2) I might have provided too many incentives, which attracted some unwanted attention. What can I do to filter out those who just come for the gift cards and interview some people of my true target?