This is ideally suited for people who are within 30 minutes or so of a populated area. Good access roads are also a factor as no one wants to get stuck in the mud with their car. However if they do, you can pull them out if you have a tractor or a 4x4. A fee could be asked for doing so.
For parking for the vendors you will need a dry field and one which is quite level. Here the grass or weeds should be kept short. Customer parking should be close by and also as dry as possible.
Organize this well and this can be a year round money-maker. You can move the location to different fields as required.
I personally loved going around car boot sales when I was in the UK . Everyone loves a bargain and they will seek out areas where they can go to several vendors at one time.
If you are in the USA, you'll know the popularity of garage sales. This is the same idea but people love to have everyone in one place.