I heard from people that during peak holiday season the VAT refund queue in Paris can be very long. I once asked a stewardess friend to help buy in Paris and she warned me that because they have strict timings to follow to check-in plus if happen to be long queue at VAT refund counter, she may or may not claim VAT refund. Had a few other friends mentioning abt long queue also.
So when i went Spain on group tour, i told the tour guide early abt my intention to 5 LV bags and fortunately he also quite 'on' abt such shopping so he made it a point to ensure that during the entire trip, he will point out where got LV and when we will be going to the next outlet and whether i should buy at Madrid or Barcelona...etc...on the last day at airport, he ensured me that Spain airport VAT refund queue not long plus as group tour, we will all need to be there VERY early anyway so no worries...but i guess at the end of day very important to let your tour guide know of your intentions so he may provide useful tips along the way