The scam accusations are against every casino and it's not like they don't face these situations but the community checks how they well they handle it.They have been distributing huge rewards to the players and have gained reputation of legit casino so they won't indulge themselves in any of these scam attempts but still there are people who can't handle gambling and start such accusations.
Counting valid scam accusations only as we can not consider invalid scam accusations as bad factor for a reputation of casino.
Like if you are a good person, you will have both people who like you and people who hate you. Even you don't know them, they still hate you and they will do something you never imagine to attack you.
A trusted casino surely has many invalid scam accusations against them. Because they are big and have big budget for promotions which attract abusers. They come to abuse generous promotions from a big casino and think that they will be able to withdraw money after that. They can succeed at their first time but later casino will pay more attention on suspicious accounts and terminate them. Withdrawals will become impossible and invalid scam accusations will appear from abusers.