Rouler dans la farine is one of my all time favorite French expressions. The expression translates literally to “to roll in flour” and means “to rip off”, “take for a ride” or “take to the cleaners”.
rouler dans la farine

Expression origin
According to expressio.fr, the meaning is simply to dupe or lie to somebody. The site suggests that actors in nineteenth century used to use flour as makeup and would dupe people with their identities.
In the reflexive form, se faire rouler dans la farine means “to get ripped off”. This is often shortened to “se faire rouler”.
Example sentences
This first example sentence is the the reflexive form: se faire rouler (to get ripped off).
J’ai trop payé pour ce vélo d’occasion. Je me suis fait roulé dans la farine !
I paid too much for this used bike. I got ripped off!
This second example is in the non-reflexive from: rouler dans la farine or “to rip off”.
Nous avons trop payé pour la voiture. Le concessionnaire nous a roulé dans la farine.
We paid too much for the car. The dealership took us for a ride.