GearScore is an incredibly worthless statistic. All it means is that they were present in a raid when a piece of loot dropped, and they won it.
If someone is fully decked out in heroic gear, you don't need GearScore to tell you they're probably a decent player. If someone doesn't have the gear you "want" them to have, you have no idea *why* they don't have it. A good player can generally play well above their actual gear score, and because nearly all fights are more about execution than raw numbers, gear doesn't even matter in most cases.
Also, it's worth pointing out that the gear you "want" them to have can easily be the gear you "expect" them to have. When running heroics, I'd sometimes get complains that I didn't have any "tier" gear or other epic dungeon drops (other than my tanking sword and shield). Everything else I'd wear my area gear, with the shoulders switched to PVP shoulders filled with tanking gems and enchantments (switched a few other things out for enchantments also). The point being, I had spent the time gaining PVP points to get duplicate items and gem/enchant them for tanking, during a periods were many others would hang around Shat and try to get a group that would carry them through in the hopes they'd get some gear out of it.
Properly researched and with the right gems & enchantments, I comfortably tanked all the heroics and a few 25 player instances BEFORE I started to see any of the "expected" warrior tank gear drop (and when it rained it poured, thankfully). During that period, though, there was often someone in a pug who'd criticize me about my choice in gear, and it was always someone who'd never played an end game warrior (and they were usually pretty green to end game).
For example, I never told a priest or a warlock how to properly gear and spec (unless that player was joining one of my arena teams), as I felt I had no lecturing someone about a class I didn't play. If a pug kept wiping, it was easy enough to tell where the problem was, and I'd try to commit that player to memory as someone not to group with again.