WARNING, the choice of the operator of diagnosis is the sole responsibility of the owner seller or lessor.
Don't let anyone decide in your place.
Pursuant to article R. 271 - 4 of the Code of Construction and housing (paragraph c), you are responsible for the selection of the operator in real diagnostics that you missionnez! In case of wrong choices, you incur a sanction criminal (1500 euros) and you risk the questioning of the contract of sale or rental (risk of cancellation of the sale)
You are responsible for the control of compliance with the legal criteria of the real diagnostics expert you call
Article R... 271 4 CHC provides criminal penalties for persons involving a professional does not meet the legal criteria: contravention of 5th class (i.e. 1500 euros).
On the other hand, article L. 271 - 6 of the CHC is of public order, the contract that binds a practising professional illegally to its client (the order) is zero. Without this contract which defines the scope and the nature of the intervention of the expert, it will be more difficult to the payer to obtain repairs where professional misconduct would have caused him harm any.
Finally, the diagnosis made by a professional not having prescribed qualifications are nullities. Everything is therefore as if they had not been made. With consequent risk to the payer seller or lessor of not be exempt from its guarantee of hidden defects, while he felt often in good faith, protected by the expertise of a professional and was thought to have done the required diligence.
You compare and decide, without losing sight that in case of dispute, your liability could be sought. But if you prove that you have all implemented to secure the services of a qualified professional, the judge will take this into account in case of problems.
A few times to save bits of candles at the outset, exposure to high financial risks is not worth the candle