Level, grimoire, communication and gear. If I see a level 7 with 3000 grimoire score, I know that they have other characters. If I see a level 32 with a grimoire of 1800, I can surmise that they're relatively inexperienced with the game. In a game (let's say pvp), I see a level 34 Hunter with a leveled celestial nighthawk equipped, I know that they're not going to take the match seriously or be very experienced.