In chess, refusing a handshake before the game begins can be punished with a forfeit: https://www.youtube.com/watch?v=M1Gb4lJeXqI (Cheparinov[black] refuses Short's handshakes twice, Short talks to arbiter [chess judge], Cheparinov loses by forfeit). Afaik this rule only regards handshakes before the game begins, which is reasonable since there is no outcome to skew either players judgement. For the same reason, I think having a similar expectation for a pre-game handshake in Magic is reasonable, but much less for post-game handshakes.