In my opinion both players should agree on every map. Btw, if U agreed to play bo3 and he quit, U have right to report 2-0 or wait for next occasion to continue this game.
he agreed to play onl I asked for a map change, he didn't agree, so I accepted it. He lost, in round 2 I asked for a map change, he didn't agree again, I wrote that once he chose, once I have the right to choose and if he doesn't change then I'll put the result 1:0, he closed the game and left xD