i played CS competitively and the cheating was horrendous. if i had to put a number to it, i would guess that 50% were cheating in some form simply because it wasn't very difficult. I would ultimately be relying on checking the number of digits in your Steam ID to tell whether this account was fresh (higher probability that you bought a new one and were cheating). I think the anon matchmaking is the horrible part, not the anti cheat software.