about buying LV in Paris

Sorry i cannot type Chinese here.

I'm posting a question for a friend's parents. They will go to Paris in 2 days, and would like to know is there any discount to buy LVs in France?

1. They heard Lafayette gives 10% discount, is it true?

2. Also, how much tax return can you get? If you buy over 1,000 euros?

3. Is there a difference in getting the tax return from the airport vs. the store?

4. Any recommendations as to where else should they purchase LV besides Lafayette?

Thanks alot.