Is it customary to tip at a french cafe?
You can but it's not obligatory. If you are served directly at
the bar, rather than sitting down at a table, it's less expensive.
This because a serveur or serveuse has to come and serve you - the
service charge is included. You also pay more when you sit outside
on the pavement (à la terrace), or past a certain hour towards the
end of the evening. If you wish to smoke, you must be served
outside. They will always present you with a small plastic or glass
saucer to place your payment on (often with a receipt) and once you
have paid - with or without the tip - the serveur/serveuse will
turn it over to show that you drink has been paid for.