Michael Jampel sends the following tip:
If ever you are in Valence in the Rhône, there is a newish restaurant in the main square near the cathedral called La Cuisine which has a policy of marking up wine a fixed amount per bottle, not a multiple of the merchant’s price. I saw a Hermitage-la-Chapelle on their list for about £5 more than it would have cost me to buy from a wine merchant in the UK. I checked with the waitress and she said it was an intentional policy by the owner to encourage people to try more expensive wines. I don't know how long this will last!