This is all way too complicated and you are writing far too many words.
Why haven't you simply told the supplier that there are risks and that you won't be held liable, and asked him to agree to that. Why should the punters' here fund the risk? - there's more in it for the supplier (especially if the thing shapes up)?
Its a good idea in principle but I can't understand why its all so fussy.
Just get the thing and try it yourself and then lend it out to whoever you feel ok about. If they are forum members the risk of being outed if they breach your trust will keep them honest. Stick to established and reasonable term posters and you will be right. The worst that can happen is that you have to tell some chap in China that his 'scope broke. Tough cookies.
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