As like most aspects of French life these are very tightly regulated, it is unlikely that you will find "Fake" goods that seem to be all to common in the UK.
Everyone having a tables at these events have to give full details to the organisers which are in turn made available to the authorities, tax inspectors etc and there is a limit to the amount that you can exhibit in one year.
If you take a table on a personal basis rather than a "trader" all items have to be owned by yourself ( no reselling ) also the maximum amount of times you can do this is two times a year! The penalties ( It is a criminal offense to exceed twice a year ) are severe with a maximum 30,000 euros fine and six Months in prison.
we visited quite a large one in the sports hall at Pleyber Christ which is about 30 min drive away from where we live on Sunday.
we came away with a nearly new expresso coffee machine for 5 euros, a bargain If ever I've seen one. At that price I didn't try to knock the price down.