I was accused of cheating once years ago. It was for marked cards which is a little different than what most people in here are talking about, but still, being accused of cheating is still being accused of cheating. I believe someone after playing me claimed I was getting all of my cards when I needed to(I was playing GG at the time, and anyone whose played that knows when you get two supporters a turn, it's pretty easy to get your cards out), and when I got towards the end of swiss, the judges checked my deck, let the owner of the store check my deck, then told me I was DQ'ed from the event. For the record, no, I didn't cheat.
Now I'm not upset at the judges for making the decision they made..ultimately at the time I didn't have a deckbox and I would just put my deck in my pocket, so my sleeves would get somewhat damaged. So to me, I put myself in a position to where I could have been DQ'ed..which is my own fault. At the end of the day though, I still was a little disappointed in everyone involved. I never really got fully embraced into the community I was playing in, so I understand that everybody may not have known my character or my intentions, but to me the second we start assuming that everybody is out to cheat, is the second we try to make the game into something it isn't, and are guilty of violating SOTG ourselves. Though there are prizes(sometimes huge ones) if you win, what people have to realize is that this IS a game. And though I'm not condoning people using certain advantages to get forward, it really ruins the game to me when people always want to expect the worst.
Like others said, let the judges handle those situations if you really aren't sure, because there's a difference between doing that and yelling out "Hey you cheated!" when you really don't know someone's intentions. For me personally I handle the situation like I do basically everything in life..I'll give you the benefit of the doubt the first time, but if something similar happens again, then yea regardless I'll probably just call a judge over and get it sorted out.