A musallamah from dialectic is a premise conceded by an opponent for the purpose of a dispute, whether or not the proponent independently endorses it.
A maqbūlah is accepted primarily because of trust in the source. It does not require a particular opponent or a formal concession.
“By your own admitted principle, you must accept this consequence” illustrates a dialectical concession.
“Experienced practitioners recommend this method,” accepted because of their trusted standing, illustrates the rhetorical use of an accepted report.