The Manu Smṛiti is mentioned in a lot of other scriptures, but it is not ever truly endorsed, unlike other scriptures. In the Manu Smṛiti, Manu says he got it from "the Imperishable One," which is a strangely ambiguous source. In fact, as discussed in this question, the law from "the Imperishable One," contradicts the general law, which implies it is not from a primordial deity. Also, the Manu Smṛiti references what Manu himself said, which means the "the Imperishable One" did this after Manu was born, which would seem weirdly late for a primordial deity to do.
वैश्यं प्रति तथैवैते निवर्तेरन्निति स्थितिः । न तौ प्रति हि तान् धर्मान् मनुराह प्रजापतिः ॥ ७८ ॥
vaiśyaṃ prati tathaivaite nivarteranniti sthitiḥ | na tau prati hi tān dharmān manurāha prajāpatiḥ || 78 ||
For the Vaiśya also these three should cease,—such is the law; since Prajāpati Manu has not prescribed these duties for those two (castes).—(78)
Is there anything in scripture that details the character of Manu? Is he honest and helpful or is he deceiving and unhelpful like Indra, and his words should not be taken at face value?