There is a common assumption that once a person goes to a Rabbi for a rabbinic ruling, he cannot turn to a second Rabbi to seek a “second opinion.”
The basis for this assumption appears on today’s daf (=page). The baraita teaches that if someone approached a Sage for a ruling regarding a question of ritual purity and the ruling was that it was impure, he should not turn to a second Sage to see if he would rule it pure. Similarly, if someone approached a Sage for a ruling regarding a question of whether something was permissible according to Jewish law and the ruling was that it was forbidden, he should not turn to a second Sage to see if he would rule it permitted.
Tosafot argue that there is no prohibition against turning to additional rabbis in an attempt to clarify the matter. They claim that the intent of the baraita is to ensure that the person asking the question will let the second rabbi know that a first opinion had already been given. The onus is on the second rabbi to make sure that when he offers his ruling, he takes into account the reasoning – and dignity – of the person who first offered a response to this question.
According to the Ran the main problem is the dignity of the first rabbi, so if the second one were to engage the first in discussion of the matter and were he to agree to the arguments of the second rabbi, there would be no problem whatsoever.
A different perspective is offered by the Ra’avad who suggests that the first ruling creates a situation where the object being discussed has been declared forbidden, and that status cannot be changed (according to this, the rule would not apply to situations of monetary rulings, where there are two sides in the matter). The Me’iri points out that even according to this approach, the only problem would be if the second rabbi were asked to rule on the exact same case that had already been decided. If, however, a different, but similar, case is brought before him, he has every right to offer the ruling that makes the most sense to him.