Players with high starting rating

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Avatar of sylwesterw

I often play with players whose ranking history looks strange. Weird is that they have much higher ranking in first days than later.  For example this player: https://www.chess.com/stats/live/rapid/finalsentinel/0 in Rapid had highest ranking in 15.12.2014. Then his ranking fell rapidly 

Does this mean that the player was cheating at the beginning or was he very lucky?