Yes, but jumble sales, or the ones I know off, are selling donated goods to raise money for charity so all income goes into the pot at the end.
Most car boot sales charge for entry too. And auto jumbles, and boat jumbles, and any other hobby based buy/sell/swap meet.
Bear in mind private stall holders don’t ‘make money’, they’re just selling their old stuff like they do on the classifides here. The Swinely one I just about sold enough to make it worthwhile (cost of postage Vs cost of the stall).
Having said that, a fiver is a lot, most autojumbles tie themselves in with a car/bike show of some sort. Having said that car shows are even worse, last one I went to I had to pay to get in, and pay to exhibit a car. I almost told them to shove it but there was a car park charge that wasn’t much less than the show charge.