before i became staff, i used to catch bypassers by first seeing if their bypassing igns were similar to their banned one. for example, HEROBRINE_345677 (banned ign) and HEROBRINE_345677 (banned bypassing ign). not all bypassers make their bypassing igns similar to their banned one tho- some can be pretty smart! but sometimes bypassers will use the same skin! take this report by
@dreaa and mine as an example:
https://brokenlens.xyz/forums/threads/bypasser.119926/#post-953031
https://brokenlens.xyz/forums/threads/bypassers.119904/#post-952807
this banned player, xXLIFEXx had a different ign but by having a similar skin it was easy to know that it was a bypasser!
sometimes bypassers can be really, really smart, that they'll have a whole different skin and name! that's where we come in! if you're having a feeling that someone is bypassing we'll check all of their bans and try to find something! i sometimes even have difficulties trying to see whether someone is a bypasser or not (since they've seen to have a good job hiding) but after a little help from higher staff that's where i ban them!
i think most people with ranks tend to check if someone is bypassing or not by using /stats >username<
i hope this helps!