Certainly context is relevant. Understanding who is saying something and what their motives are helps you to judge how likely facts are to be true, and how much

Certainly context is relevant. Understanding who is saying something and what their motives are helps you to judge how likely facts are to be true, and how much weight you should attach to opinions. Calling some work into question because of the authors' motives isn't a claim that some other group has no ulterior motives at all. Certainly everyone has some motives, otherwise we would never get out of bed. But some of those motives will change the discussion more than others. E.g. when HP sponsors a study that finds that their own ink works out cheaper than buying remanufactured cartridges, it's perfectly sensible to be more suspicious of that than if a study by a consumer organisation found the same thing.