Do we know for sure that BPS, GET or brain retraining doesn't work for everybody?
Of course we know it doesn't work for everybody as this has been shown in multiple trials. The existence of this website is proof that it doesn't work for everybody. I think what you're trying to say it doesn't work for anybody. But there no argument there. The trials have shown there is no worthy benefit to it. I really don't see what you are trying to argue here. Whether or not something works is not a question of whether someone believes it works but depends on the evidence. It seems you don't seperate "works" from placebo-effect, regression to the mean, natural recovery, Hawthorne like effects, adapted behaviour, selection bias, subjective outcome measures, no long-term follow-ups, reporting bias and all other things? Is that a meaningful definition of "works"?
Would you argue similarly by saying that cutting off someone fingers "works" against Alzheimers because that person afterwards responds to a questionnaire by answering they don't remember having Alzheimers because they aren't able to remember much? Does ice cream "work" against MS because someone says they are feeling good after they had one. Is that your definition of "works"? You cannot establish what "works" or doesn't without solid evidence. That is the whole point of clinical trials.
Do we know for sure that BPS, GET or brain retraining doesn't work for everybody? There could be one or two out there with anecdotes.
What do you mean one or two with anecdotes? We know far more than that with anecdotes. There's studies on them and there's also other studies on supplements such as
Patient-Reported Treatment Outcomes in ME/CFS and Long COVID. There's also websites to collect all thses anecdotes (Eureka Health for example). The problems with such anecdotes have been discussed at depth.
As much as I think they don't work, I wouldn't take it off the table for all.
Are you suggesting one should ignore evidence and doctors should treat someone with cancer with voodoo because they read on facebook that it would work and because they believe in it, rather than chemotherapy?
Their improvement could even be real.
Nobody is arguing that people with ME/CFS can't improve or that there aren't instance where improvements can't be real. We know they can. It has been seen in trials of medications without efficacy as well.
I'm really not sure what your argument is. People can do all sorts of esoteric things they want, they already do it and nobody is hindering them. Most people try GET because it's natural to think that one just has to do some exercising, apart from that the rest which is anyways typically forced into doing it. Offering services without evidence to ill people is the problem.