They Treated As Avoid

بِسْــــــــــــــــــمِ اﷲِالرَّحْمَنِ اارَّحِيم

It is obligatory for a follower to learn the Masae'l which are of daily importance.

If a person faces a problem whose rule is not known to him, it is necessary for him to exercise precaution, or to follow a Mujtahid according to the conditions mentioned above. 

But if he cannot obtain the ruling of an A'lam Mujtahid on that matter, he is allowed to follow a non-A'lam Mujtahid, even if he has a general notion about the difference between the verdicts.

If a person relates the fatwa of a Mujtahid to someone, and then that fatwa is changed, it is not necessary for him to inform that person about the change. 

But if he realises after having related the fatwa that he had made an error, and the error would lead someone to contradicting the laws of Shariah, then as an obligatory precaution, he should do his best to rectify the error.

If a person performs his acts for some time without taqlid of a Mujtahid, and later follows a Mujtahid, his former actions will be valid if that Mujtahid declares them to be valid, otherwise they will be treated as void.

Allah Knows The Best