Those two guys are interesting conversation pieces, since if you look at their physiques you can say they could be using or they might not be and are just that big, because yes, both obviously used and both looked like shit, although Barnett is a result mostly of odd fat depositing by his body and a classic case of too much estrogen crossover (bitch tits he had removed which is why his pecks look so weird), Sylvia just looked like shit in general. But you could say maybe even if they hadn't been caught.
The giveaway for guys like that is the face. That bloated roid face-that Gordon so clearly has-is what tells you Sylvia and Barnett were using. There is also the classic growing of a beard to cover up the bloat face and the post-career fattening up that is way out of proportion even with the reduced activity levels taken into account (Sylvia is a good example of this).
I never saw Marcelo with any bloat, suddenly working a beard for years, odd physique attributes like obvious surgery on his pecs, or any fattening up when he stopped competing.
And both Barnett and Sylvia had pretty typical personalities for fighters and maybe that's just who they are and wasn't the juice, but imo Marcelo would never have been able to show zero signs, physique, face, personality, that he was juicing. You're always going to see it pop up somewhere.
The average gym goer, even the gym rats, are not engaging in physical activity anywhere near the level of ufc/adcc competitors, but even then I've never seen a true gym rat who looked like shit. Maybe the typical chicken legs and big arms, maybe the bloat cause they don't want to cut and lose that precious size they think makes them manly, but never like complete shit. I think you're talking about the trt dudes who have no idea what they are doing in the gym or the kitchen, those guys are pretty common.