Compare rents of flats with standard legal rents
In some cities in France (especially in Paris, but in other ones as well), the monthly rents of housings is regulated and cannot be above some given threshold.
It could be helpful to compare the price of the fetched housings with the legal rents (they should all be below) and put an indicator of how high is the rent compared to the mean for the same type of housings (based on cost per area for a beginning for instance).