Answer:
It could be argued that there is a separate force acting upon the investigation. Or that the room is invalidating the results for some reason. Or that an error was made in measurement.
There are a thousand and one ways to try to dispute an investigation like this. However, for every argument that can oppose it, a counterargument can easily be made.
For instance, controlling the variables invalidates about 90% of any possible claims to the contrary. The majority of arguments would stem from the fact that it is nearly impossible to completely prove something in fear of external factors. The solution? Control the external factors.
So, in conclusion, a person could dispute the results of the investigation by claiming that something invisible like magnetics could not possibly be proven to exist, because there are all sorts of things that could be influencing the investigation. The way to counter the argument would be to prove yourself that the environment is controlled, and that nothing could be influencing the investigation.
