Heatmaps, trends, rent controls. The information that makes the difference.
Median price in the neighborhood is 1250€/month. This listing is 12% above market. Now you know.
12-month price curve: +2% in this neighborhood. Trend is up. Decide with full knowledge.
Auto comparison with rent control caps. This rent exceeds the limit by 8%. Negotiation argument.
In practice
An apartment is listed at 1400€/month. Is that expensive for the neighborhood? You have no idea.
Median price in the neighborhood is 1250€/month. This listing is 12% above market. Now you know.
You want to buy but hesitate to wait. Will prices drop?
12-month price curve: +2% in this neighborhood. Trend is up. Decide with full knowledge.
The landlord asks 25€/sqm. You don't know if that's legal in Paris.
Auto comparison with rent control caps. This rent exceeds the limit by 8%. Negotiation argument.
Buyers and renters negotiate blind. With market data, you negotiate from a position of strength.
Mansard