enlighten us, how would you stop this issue! Don't say "Just check if they made 5 sc together or where in the same guild during the last 5 years". Give a waterproof concept!
Most of the detractors here are not able to distinguish a premade from a pug group even if they would name their chars "Iamapremade1-6". As mentioned before, just because people are rearange groups at the beginning or do such horrible things like assist and move together only means they know what they do.
A big factor in pug sc is the amount of 2 man groups, two people playing together with voice, assist, guard can easy take out a 6 man of random dudes without a plan and healing. I often play solo myself, and I hate if I get stomped, like everyone else, but in most cases there is no way to determine if the enemy is premade or just plain better.
Edit: Just courious, where would all the 3-5 man play in a world where it's only pug or 6man