Joseann
In France, the seller has to let his house go if the prospective purchaser offers the full price. And there is only a 7 day cooling off period before everything is then signed.
Joseann We sold our French house in (22nd April) this year and there was considerably more than a fortnight between making the offer and , essentially, exchanging contracts. It is also possible to put conditions on the offer and acceptance, as we did this when we bought in France, we intitially offered on a house on condtion a problem was resolved. When this wasn't, we were able to just walk away.
More genetally, I quite agree when an offer is made and accepted and negotiations start, the property should be taken off the market, but here can be so many provisos,, doubtful points, re negotiations on the buyers part that the vendor has to protect themselves and sometimes this means keeping the house on the market (with the person who has offered knowing this.