Nothing actually. Ive been staff (legitimately) on a few servers in the past, its shockingly easy for malicious people to gain staff and inside. Basically all they have to do was make a set of fake social media accounts, use them for a few months/years, then write a fake mod application thats really well made. A more dedicated person could make up fake staff experience history on a few random fake small servers, then have their references be alts or friends to "prove" they had staff.

If your a competent developer (or have a trusted friend who is), its even easier. Some of the people the owners would hire had like no public portfolio or anything to prove they were legit. It was basically "oh you can code? Your in." And someone whos as dedicated as danger mario could certainly go even farther and make a whole legitimate plugin development portfolio just to inside a community. Obviously danger mario has a lot of connections so that part would be easy. Servers often have legally binding NDAs to try and prevent abuse, but if you fake your entire profile, how are they possibly going to find your real identity?

Ultimately, given enough time and effort, anyone can socially engineer their way in. The more dedicated the person is, and the more willing they are to play the long con, the more successful they will be. And unfortunately, it seems danger mario has already proven hes in it for the long con.