Why was Lavan skeptical?
Hadar Zekenim: He was concerned lest Yaakov retract. 1
Ohr Zaru'a (1:769): It seemed that it was a small amount.
Bechor Shor: This is why he removed the animals the same day, before Yaakov will retract.
QUESTIONS ON RASHI
Rashi writes: "Lu Yehi chi'Devarecha - If only you will want this!" What is Rashi explaining?
Gur Aryeh: The verse uses the perfect-future tense 'Lu Yehi,' rather than 'Lu v'Hayah.' Lavan was afraid lest Yaakov retract, and he said, 'If only you will [still] desire this arrangement later on!'