Given the overcrowded research market where many researchers are competing over the same participants, researchers are considering novel ways to recruit them.
One way is to make some form of incentive, like draw on a prize, or a voucher, or a free visit to a clinic. In this video I discussed this practice from an ethical point of view.

I believe it is ethically problematic for a few reasons. First, it makes us in doubt about the voluntariness of the participant’s decision. Second, it creates an unfair and unbalanced competition among researchers. Thus, research participants will favour studies with bigger incentives, which will make the researchers make their incentives bigger and so on.
For the full discourse, please watch and leave your comments and views here or on YouTube.