It is difficult for a while when you change tier, as already suggested play all the courses, progress at your own speed and don't get stressed about a few players who think winning is more important than playing fairly. Not that all the low scores posted are sandbaggers of course, there are some players who are just very good at this game.
It's hard for WGT to do anything about sandbagging though, who can prove that someone who shoots mostly 60 and suddenly has an 80 round did it deliberately. It can happen for real. I posted a 44 for BPB front 9 recently after taking a 10 on the 3rd hole and totally losing concentration after that. That's 16 shots more than my best single play effort there. By the same token you might have someone who shoots a great round out of the blue and wins a competition, it can happen.
The best advice I can give is to let them get on with it, work on your game at all the courses and enjoy yourself. Once you make legend you've left the sandbaggers well behind.
And above all, never, ever play one of those players in a challenge game for credits. Any time you get a challenge sent always check that player's profile. You can right click on Community to open in a new tab so you keep the challenge open while you check them out.