A Hossid will give you15 answers to a single questionA Litvak will give youa single answer to 15 questions.
Here are two related knotty problems.
In Hayyei Sarah, Avraham assigns Eliezer to find Yitzchak a mate. The Talmud admonishes us that we should not act the same way since Eliezer's technique involved "Nichush." If so, then how could Eliezer use this means to select a proper shidduch? Alternatively, how can it be that Yitzchak's great match was manifested through such "under-handed" means?
Similarly, in Toldot, Yaakov "usurps" the brachah from Esav via deception.One may not excuse Yaakov's behavior on the grounds that he was obeying his mother, since one may not violate Halachah on the say so of a parent. So how was Yaakov permitted to engage in such a masquerade?
My approach is similar and simple. In each case, the alleged offense was committed under the instruction of a Prophet/Prophetess; Scripture actually makes this quite clear on a P'shat level
Avraham told Eliezer that a Malach will accompany him and that Hashem will cause him to succeed. Given this CONTEXT, his Nichush was under Divine Providence and therefore did not involve superstition or "dark forces"
Similarly, Hashem told Rivka [directly so - if we set aside Rashi] that "Rav Yaavod Tsa'ir." Given that this n'vuah is also in the text, her command to Yaakov is therefore that of a prophetess and not simply that of a Mom. Yaakov is therefore engaged to commit this deception in this extraordinary circumstance.
This also explains why the text orders these Prophetic pronouncements just before the questionable behaviour. It does so to set up a proper context so that we would understand the dynamic here and not learn the wrong lessons about Nichush and deception