Here is my advice on visiting a rural vide grenier in France, based on my own experiences!!!!

Have cash - preferably in small denomination notes. More convenient for the sellers if they don't have to give change.

Be an early bird - arrive early - catch those worms - find those bargains! They will set up from 5am onwards! Bring a flashlight or torch!

Be prepared to rummage - they may not bother to put everything out and display it nicely - look through boxes. Be thorough - look under the tables for those gems.

Ask questions - they may not have put everything out, and may have just what you want sitting in the back of their car! 

Come prepared with your own bags, or trollies for transporting your purchases. When vide greniers are held in the villages, the roads are usually closed off, with the approach being choked with parked cars on grass verges on both sides of the road.

In my experience if you arrive after 9am you will have to leave your car quite a way from the village, which leaves you a long way to lug your treasures back. If your bags or suitcases, or trolleys have wheels they are much easier to trundle back to the car with than a heavy bag or box, then empty the trolley and return to shop some more!

In a rural area as my own, the items are priced for the locals, and bargaining or attempting to get the price knocked down is really not popular except when buying in bulk, when the sellers are happy to discount without being asked. It is easy to offend!!

Lastly, enjoy!!