There's a lot of trust with these 'bribes', of course the people can take the money and then vote for whoever they want.
So, these people are corrupt enough to sell their votes (which they very well know is wrong and illegal), yet they are HONORABLE enough to actually stick to their end of the bargain when they full well know they don't have to?
Sorry. You can't have your cake and eat it too.
Of course it is true that politicians hand out goods and possibly money at their rallies. They do it knowing full well that there is ZERO guarantee that they will actually get anyone's votes.
Just like in other places politicians may offer welfare aid knowing full well that the people who get it may vote against them. It is of course a lot more expensive to give people life-long welfare aid than to hand them an election-days gift (cash or whatever).
In either case, the voters may take the giveaways and still vote for whoever they want.