For a random consumer opinion I dont think collecting marginal payment on sales leads hurts credibility per se. The huge red flag for me is taking payment from manufacturers. But an adequately disclosed commission, applied equally to different masks, doesnt obviously introduce bias in to your test results. I guess it could induce you to recomend higher priced masks. But readers have the qualitative data available to select comparable, cheaper, products as well.

Perhaps you could provide two links. Once with affiliate tag and one without? Give users the information and the choice.