from what I've seen in actual vrg hangouts, people call someone a groomer if the following happens:

1. newfriend starts hanging out with vrg anons
2. oldregular approaches the newfriend and acts very friendly to them, while wearing a lewd avatar and getting into lewd positions
0. oldregular is known to have erp'd at least once in the past, and are assumed to be interested in erping with the newfriend

other vrgers point of view:
oldregular is being fake-nice to newfriend just to erp with them, and they'll stop being fake-nice after they get what they wanted, resulting in hurt feelings for the newfriend

oldregular's point of view:
erping is fun, it makes sense to be nice to someone if you want to erp with them, nobody will want to erp with you if you're being a rude prick to them. this new person has a trait about them that makes it seem like erping with them would be fun, such as their avatar, voice, personality, or any combination of those, so it makes sense to be nice to them

newfriend's point of view:
was hanging out with vrgers all alone until now, nobody talks to you, you sit in the corner and feel lonely because everyone already knows each other and they can't be assed to talk to a new guy when they can just talk to their old friends. suddenly someone is being nice to you and invites you into the group, lets you participate, pays attention to you, you don't feel alone anymore. plus you get free sex on top of it later on

are groomers the bad guys!?

if the qualities that newfriend has that made oldregular show interest in them are genuine (i.e. they were into you because of your personality) oldregular will probably keep being nice to newfriend forever

if the qualities were fake (they were into you because of your avatar, but later on realized your personality sucks, and at that point your avatar doesn't matter anymore) then oldregular will probably ditch newfriend

how this is the groomer's fault? it feels like the ball is in newfriend's court