There are several possibilities especially after seeing how hard, scary, and devious Laban was during Jacob’s later confrontation with him in chapter 31:
Genesis 31:29 “I have the power to harm you; but last night the God of
your father said to me, ‘Be careful not to say anything to Jacob,
either good or bad.’”
Genesis 31:41 "It was like this for the twenty years I was in your
household. I worked for you fourteen years for your two daughters and
six years for your flocks, and you changed my wages ten times."
Genesis 31:5-7 “He said to them, ‘I see that your father’s attitude
toward me is not what it was before, but the God of my father has been
with me. You know that I’ve worked for your father with all my
strength, yet your father has cheated me by changing my wages ten
times (a biblical way of saying "a lot of times"). However, God has not allowed him to harm me.’”
During the Betrothal
When Jacob asks for Rachel’s hand you can almost see Laban’s wheels turning in his response. Instead of explicitly agreeing to the betrothal Laban says:
Gen 29:19 “It’s better that I give her to you than to some other man.”
It’s easy for us to impose our ideas of courtship on their situation. But this is the ancient near east; marriages in their culture were arranged and heavily managed by the father. We’re not told they spent considerable time together. Instead, here's Jacobs summary of the time between the betrothal and marriage:
Genesis 31:40 “This was my situation: The heat consumed me in the
daytime and the cold at night, and sleep fled from my eyes”
It seems Jacob wasn't spending his time in the comforts of Laban's home. Instead, he may have been away taking care of Laban's considerable estate.
Wedding and Consummation
When Jacob demanded that Laban stop withholding Rachel, Laban ignored him and instead, ordered a party, presumably to get Jacob drunk, so he could pull off his deception.
While not recorded in the bible, tradition has it that it that Leah was wearing a heavy veil during the ceremony. In fact, Bedeken (בֶּדֶקֶן) which means “to veil” is a modern Jewish ceremony where the groom checks the brides face and places the veil himself to avoid a Jacob situation. Centuries of tradition seem to indicate this is how many Israelis interpreted this passage.
Also, Laban waited until evening, using the darkness to trick Jacob into laying with Leah. The party and the cover of night all seem to be part of the deception, perhaps blamed on local customs as Laban later uses as an excuse:
Genesis 29:28, “It’s not our custom here to give the younger daughter
in marriage before the older one”
Some oral traditions have it that Laban also refused candles, citing local customs. In this case, Jacob may not have been able to see his bride. Sadly, we don't have sufficient details to know what happened for sure. Traditions such as the bedeken (veil ceremony) and ancient Jewish commentaries can shed some additional light, if not add to the speculation:
The Midrash, a genre of rabbinic literature or commentary, interpretation, and elaboration on the Hebrew bible holds that Rachel was in on the deception, telling Jacob beforehand that Laban would pull this trick, providing him with symbols to know if it was her or not, but then later withholding the symbols to avoid shaming her older sister.
However, it's unclear then if Rachel's later rage was a righteous or jealous anger, as she seems to hold Leah accountable for taking Jacob:
Genesis 30:15 "Wasn't it enough that you took away my husband?
That said, the midrash isn't the only rabbinic commentary on this. There are oral traditions around the retelling of this story that could expand the possibilities further, if reliable.
