How to judge a candidate who has accepted your salary offer and does not join on the date of joining?

IIndividual is the best judge for himself interest, individual have a right to reject even after accepting you offer, but for respect & sense of humanity  at least he/she must call to apologize and give acceptable reason for not joining according to accepted date .

check with him

maybe he have any emergency or reason after that give him warning if he do it again without any reason through training period just fired him