Background : to figure out how many buyers I was competing against in FR - and check if the resale prices demanded by Audi agents were in line with the buyers- I simulated a selling ad for a Grey Avus + Sat Nav with 50-60 000 km and 12-month warranty.
I used the print and web magazine La Centrale Des Particuliers, the absolute leader in second-hand ads in France.
I started advertising at Eur 45.6K, then 43.9K and finally 42.1K (cheapest of all ads).
Since I started the ad, the average asked-price went from EUR 54K (Jan-15) to EUR 51K (Feb-6) to EUR 49K (Feb-20).
In other words, it moved from most offers being in the 55K range (black dots) down to the 50K and under range (red dots).
Here's the chart with all offers, for the 3 consecuting dates.

Eric