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There's two things going on here:
as BQ says, people just expense the shit out of everything and the tax take drops
The French don't let anyone in* and they don't like foreign buyers; the cost of housing is largely defined by demand and there isn't any, by design, except for the obvious hot spots
The two aren't related, the policy on charging CGT on property profits does not contribute to lowering demand, it just lowers the tax take.
* in comparison to our historically liberal immigration policies
The French do this and their housing market has been stagnant/falling for 12 years.
The side effect is that people produce a lot of receipts proving they have spent more on the work to bring it up to the selling price than any profit, and they usually flog the wardrobes and beds to the buyer for €10,000 euros to reduce the headline selling price.