A great example is silicone breast implants. Millions were paid out to the "victims". There was a time when virtually everyone who had casual knowledge of the topic knew that those things cause health problems when they leak. (mass sociogenic illness - can be likened to placebo) But years later very large and long term studies came out completely debunking the notion. They are safe, period, despite the millions who claim otherwise.
They same goes for unproven claims about UV. Show me a list of 100 customers that rave. Show me a 1000. In the absence of proof they can easily be explained away as placebo. I can produce a long list of customers whose UV light was down when I arrived and they had no idea because it did nothing to begin with.