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You can usually recognize such SG's if the MOTD is along the lines of "KEEP SG MODE ON AT ALL TIMES..
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The SG I'm part of has something along those lines as a message, only less CAPS. That said, it's only been going for about a month, and we wanted/needed things like a medical bay and such.
Most of the people in it have only played for a couple of months at best. I think newer groups kind of need a MOTD like that (only more friendly) until they can get off the ground.
That said, the majority of the group are all friendly and helpful. It's not just one guy who wants an awesome base, so he can be the best. That kind of thing is silly.
As for invites, I got invited after a long teaming, and I only invite others if I've got on with them in a team or just chatted to them on several occasions. A couple have been new, and the SG can help them with the basics if I'm not around. (Not that I'm a veteran).