Illegal subletting: building the proof to act

Written by Guillaume Pouillier, CNAPS-licensed private detective, licence no. AGD 095-2024-03-06-20190240581 · Last updated: July 14, 2026

Unauthorised subletting is proven, not guessed. A listing is not enough: you must establish who actually occupies the dwelling, how often, and for what payment. Our dated findings and certified captures turn your suspicion into a case, and French case law awards the collected sub-rents to the landlord.

How do you know your tenant is really subletting?

The classic signals: rotating suitcases and faces, rogue key boxes, exasperated neighbours, a listing spotted on Airbnb or Booking, abnormal utility usage. None suffices alone. Our investigation objectifies the situation: actual occupancy verified on site, documented listings, booking calendars cross-checked against observed comings and goings.

Platforms anonymise addresses and hosts: establishing the certain link between a listing and YOUR property is precisely the technical crux of the case. We resolve it by methodical cross-checking, listing photographs matched against the known interior, availability calendars set against observed movements, neighbourhood elements gathered fairly. Once that link is made, the rest follows.

What evidence is needed to terminate the lease?

A body of evidence: findings of third-party occupancy (dates, frequency, profiles), the listing and its prices materialised, the certain link with the dwelling, and ideally recurrence. That file grounds the formal notice, then the termination action before the housing judge.

The financial stake goes beyond termination: since a 2019 Court of Cassation ruling, sub-rents collected by the tenant belong to the landlord, their restitution is claimed before the judge, figures in hand. Our dated captures of prices and booking calendars serve exactly that calculation. In Paris, undeclared tourist subletting additionally exposes the tenant vis-à-vis the City, which only strengthens your civil case.

Can the tenant turn the tables on you?

Not if the evidence is obtained fairly, which is the whole point of using a licensed professional. We never enter the dwelling, never pose as travellers beyond what case law admits, and document every finding from public space.

The line between an admissible test booking and unfair entrapment is a matter of method and case law: we know it and calibrate each assignment with your lawyer when the case heads to court. The CNAPS licence (art. L621-1), professional secrecy (art. 226-13 Criminal Code) and the proportionality principle frame everything, which is what makes the report admissible as filed.

How long does it take to build the case?

Two to four weeks in general: the time to establish recurrence, document the listing and make the certain link with the dwelling. Intensive tourist letting is documented faster than a discreet year-round sublet.

The timetable adapts to your strategy: if a deadline approaches (lease renewal, notice served, hearing), we concentrate the sessions to deliver in time. The final report includes chronology, findings, time-stamped photographs and certified captures, ready for the formal notice as for the summons. Multi-unit landlords: our tenancy investigations scale to volume.

How much does it cost?

Our assignments start at €85/hour (excl. VAT) (full day €850, volume discounts). Every case gets a free written quote before any commitment, no hidden fees.

A typical subletting case uses a few observation sessions spread over two to four weeks, plus documentary work on the listings. Set that against the recoverable sub-rents and the value of getting your property back: in most Paris cases the investigation pays for itself.

See the full price list.

Frequently asked questions