Hi Charlotte
I don't know how you actually go about it but a few years back some friends of ours who were making a very comfortable living with their market stall in UK came over to Spain to do the exact same thing.
They went back after two years!
They just couldn't replicate the success they were having back home. They were selling end of line clothes such as from M&S and Next, but they struggled to make decent money.
Their main problem was.....the weather! We had a terrible winter that year and when it rains markets are either cancelled or no one turns up to them.
I'm not saying every market and every stall would be the same but that's their story.
It can be tough, especially trying to get a decent pitch so maybe just don't burn all your bridges straight away.
Best of luck with it.