As for me when I search for french subtitles for movies I go to subscene.com website and found a decent one most of the time. Generally if you get a subtitle from a DVD zone 2 of a french movie it will be a transcript, and if it's of a foreign movies it will be professionnal translation. If it's not coming from a DVD then the quality is not warranted (could be very poor to very good). For TV shows (it's frequent but can happen also for movies) be aware that subtitles may not be word to word transcript but "simplified" sentences.