This can be a challenge, but does lead to many interesting workarounds.
The original change blindness / door experiment conducted outside a lab setting didn’t get permission from participants before enacting the test.
This had to be corrected, and subsequent tests needed participants to sign off before they could participate. If you know the experiment, you would assume that being informed of the experiment would not be conducive to the test.
The researchers found a way to still create a workable experiment. Volunteers would be able to go to a kiosk to sign up. If they signed the release (? forget the name) form the kiosk attendant would duck down out of line of sight for a second to pick something up, and would be replaced by the accomplice.
They would then direct the volunteer to the debriefing room.
No, because facts won't change their mind.
Do people who participate in psychological studies ever realize this is the case? Surely after the first time being misled by someone in a lab coat you'll be more skeptical the next time?