yes it is!
TBH, I wouldn't serve wine, you will get the swamp-donkeys and feral grannies turning up in full force for a jumble sale and wine might over-excite the two parties - though the ensuing riot might be entertaining...?
Charge a nominal entrance fee, as someone else suggested and serve teas, cofees, biccies. If you have time, contact our local NCT (might be able to rustle up a contact if you need one) as they use rails for their big secod hand sales and might be willing to lend/hire them out.
The other top tip is (having once been involved in a juble sale at fairfax comminuty centre - shudder at the memory) was arrange tables round the edges with minimal gaps for 'them' to get through loosely themed with bric-abrac, books, toys, etc and in the middle of the room, have a square of tables for clothes with helpers going in the middle. It's less overwhelming for helpers and cuts down on the possible theft of your money, as easier to keep the public out of that area, IYSWIM.