I believe they apply quantitative metrics on this one, one of them is about 'how many reported the scam channel'. So, it's not like a user reports it as a scam and they got closed down an hour later. However, it's possible that this can get abused too. I personally know at least one user who got the scam tag but later it was removed. Dunno what happens but he probably reported his case to Telegram and explain why he should not be tagged as a scammer.