Validity of a Halacha ruling

There is no such obligation. If you have already asked, then perhaps there is an obligation to listen (and I am not sure about this either), perhaps you have learned from a wise man's ruling that whoever forbids, his friend is not permitted to permit (if "his friend" includes the questioner himself). Indeed, if you asked, you should not ask another rabbi, because you are stumbling him over a wise law that a friend has forbidden and is not permitted to permit. Beyond that, you are essentially entering the realm of "this and that are evil" (asking until you find a wise person who will ease the matter). If you don't know what the halacha is, you go to a posek and you should listen to him because he knows halacha and you don't. But this is not his formal authority but from his knowledge. It's like there is no obligation to listen to a doctor but it is worth it because he understands the field and you don't. Formal authority (to listen to someone just because he said so) is only available to the Sanhedrin or a rabbi in his community (who accepted him over them).