//The owner of the business decides that they will save £20/day by not paying to attend the market.//
It depends what conditions the market imposes on you for your £20 a day. If, for example, it says that you cannot do a deal to sell your goods in another market without the first market's permission (requiring the agreement of all the other stallholders) and that any disputes about such things are settled by a panel appointed by the first market, then it may not be such a good deal. So it's not quite as straightforward as you'd have us believe.
However, I've a feeling we've been there, done that (once or twice).