Don't fall into the trap of buying straight from random websites or sketchy marketplaces, because that's how you end up with fake tickets. In practice, I always check what the official platform is that the venue is using - like, if the show is at Allianz Parque or a bigger stadium, they usually make it pretty clear which system is selling them. Between Ticketmaster and Sympla, the real difference is that Sympla tends to charge lower fees for smaller events, but for a big show like Anitta in São Paulo, both will be there and the final price ends up being similar. The safe bet is to go straight to the stadium's or event's official website and buy from there, without jumping around between apps.