HI Tschwaninger
It is not that easy, unfortunately. EU is still 27 countries. If it is a one time thing, and you friend managed to clear your items through customs , then the easiest way for him to sell using 10 000 EUR simplification available for EU based micro companies /entrepreneurs. If he does not have a turnover selling over that limit to other EU countries , he can actually sell the stuff applying his French VAT rules. If that is not the case then it is best to ask someone who is registered for Union OSS scheme and sell it through them. That seller should be registered for French VAT and OSS scheme .
Another option is place the stuff with Amazon issuing FBA in France and sell it through them.