Example of the righteousness of Yaacov mentioned in the same Gemara

Yaacov illustrates "Lo Ragal Al Leshono" - he was reluctant to deceive Yitzchak (to get the blessings) אולי ימושני (בראשית כז, יב(. How do we understand this concept from this verse?

Rivan:

Yaacov did not wish to present a falsehood to Yitzchak but Rivkah told him to do so based on a prophecy עלי קללתך (בראשית בז, יג( )per the Targum(.

Maharsha:

Yaacov did not wish to accustom himself to speaking badly of others. If Yitzchak were to find out that it was Yaacov who came for the blessing of the first born, then Yaacov would need to explain about the bad deeds of Esav that resulted in the sale of the birthright.

Mahritz Chiyos:

The intention of the Gemara is that Yaacov did not say "פן" but used the word "אולי". The word “Pen” is indicative of a strong negative. But Yaacov used the word “ulai” to indicate that he really wished to convey the truth to his father, and only Rivkah prevented him from doing so.

Aruch LaNer:

Someone who is a regular liar develops mannerisms that make it difficult for others to detect that he is lying. But someone who lies for the first time is easy to detect that he is lying. Thus, Yaacov was concerned since he had never lied before, how could he possible deceive his father from detecting the truth.