Most people do not need to exchange $ bills into € these days, if they have an ATM card.

But if for some reasons you have to sell your $ ( leftover drug money, etc ), here is a secret for you:

Use the chinese exchange shops in the 13th arrondissement. They are all mom and pop operations, and give you the best rate in town.

Today they bought $1 for €0.88.

My $900 yielded 792€.

American Express wanted to give me 702€. Thieves.

Metro Tolbiac, Avenue de Clichy, walk half a mile, you'll find them.