I have been checking GOG for longer than I have the account here, so I remember the forums from when GOG was pretty new and unknown to a lot of people. That being said, I can say that with GOG getting bigger and more known, of course a lot of "bad people" have joined in. Before, those who had rep, usually really earned it, compared to today with more people abusing these points.
So when people made give-aways or had requests about something, you could check on the respective persons rep if it was a trustworthy individual. But yes, rep can't be used as a real indicator for seriousness that much and has kind of lost its porpuse in my opinion