He doesn't have the burden of disproving it, the study has the burden of proving its claims. I consider studies funded by an interested party as weak evidence at best - perhaps enough to encourage an independent party to conduct another study.
If you can't read a study well enough to tell if the methods it uses are good, that's your problem.
You pretty much have to repeat the study yourself to see whether you get the same results.
All studies like this are "believe us when we say that we did this, and observed that".
If you're paid by X, and the result is favorable to X, then I don't believe you as much.
Is that an option that’s on the table? Or do we have to take the information we’re able to get and just interpret it critically?