The seller pays the fees as per contract, but adds these to the price of the house. In the end it just comes out of the negotiation margin. When a company says '50% goes to taxes', this is a bit like kicking in an open door. EVERYBODY with a business pays 50% in taxes. A butcher doesn't go around saying: "Yes, my meat is not cheap, but remember... 50% goes in tax." now does he? So why should a property agent use this excuse?
The problem in France is there are too many brokers sharing the same sales. Most people take 4 or 5 agents. So when the house is sold, 4 of them earn nothing. This loss is spread over the cost of the houses he does sell. So on average they earn 6% : 4 = 1.5% on each house they sell.
What it boils down to is that we, the consumers, pay for the surplus of property agents in a diseased market.
We should all choose one good agent, offer him the exclusive rights for six months, invest in good pictures and some 'home stageing' and insist on paying maximum 3%. This is a very good price, considering that he will have no competition and for 6 months he'll be certain to make this money.
You could then add a stipulation that if you find a buyer first, the agent will take only 1.5% for handling the paperwork. This gives you the right to also use the FSBO market, which consists of about 50% of the total.
As for the diagnostics, shop around! Ask your notary, who is not allowed to take commissions. I'm certain you'll find a better deal.