How does one respond to those who forbid following scholars or preachers, claiming their creed is corrupt, or they commit sins, or they weaken strong hadiths, knowing that these scholars and preachers have a great impact on spreading the Islamic call?

One should seek out a person of Sunnah from whom to acquire knowledge, and if found, one should strive to accompany him. It has been said: "Indeed, this knowledge is your religion, so look from whom you take your religion," and it was also said: "Among Allah's favors upon a young person is that he be guided to a person of Sunnah."