> Sometimes I'll play someone with a similar ranking to myself and beat them and > will earn 3 or 4 points. Then we'll have a re-match which I lose and they'll

> Sometimes I'll play someone with a similar ranking to myself and beat them and > will earn 3 or 4 points. Then we'll have a re-match which I lose and they'll > gain 12 or 15 points. It's probably a sign that they have a new account. If a player has played very few games, then his rating is only approximate. It's likely his true rating is far from his current rating. The rating added or subtracted due to a win/loss is on purpose made large, so he quickly can get to his true rating. When he gets to his true rating, he will presumably win and lose the same amount of games and stay at the rating. Lichess and Chess.com both use (variants of) Glicko (instead of ELO). The first step is to calculate the rating deviance. A high deviance means that the player hasn't settled on a given rating. This factors into the calculation of the new rating. The sites have chosen this system so that higher (or lower) rated players that make a new account quickly get close to their "true" rating.