I read law at Aix-Marseille and spent four years in notarial practice in Nice before I sold a single house. On this coast that is a less unusual background than it sounds, because every French property transfer runs through the notaire, and understanding that machinery from the inside is the difference between a sale that completes cleanly and one that drags into the following season.
The first misunderstanding is that the notaire acts for you. They do not, in the sense an English or American buyer means. The notaire is a public officer charged with the validity of the transfer and the collection of tax. A single notaire commonly acts for both parties. You may appoint your own at no additional cost — the fee is split, not doubled — and if you are buying from abroad you generally should.
The second is the compromis de vente. Signing it is not an expression of interest; it is a binding contract, subject to a ten-day cooling-off period for the buyer and to any conditions precedent written into it. Foreign buyers sign it far too casually, and then discover that the finance condition they assumed was standard was never included.
The third is timing. Between compromis and acte de vente there is a pre-emption enquiry — the commune has the right to buy in your place — and it takes as long as it takes. It is commonly a matter of months, not weeks. Nothing you or your agent do will speed it up, and any advisor promising otherwise is telling you what you want to hear.
The practical advice is short. Appoint your own notaire. Have the conditions precedent drafted before you sign anything. And build the pre-emption period into your plans rather than discovering it in week six.