Totally agree with EG. Also when customers are used to your soap they want to buy from you and not another soaper. There is not always enough soap buyers to support several sellers. I do sell a lot of soap, but sometimes I sell one or two bars and sell 10+ crochet hats, so without my additional product to sell I would go home losing money. I do not get up early haul and setup to lose money. You never know how a market day is going to go for sales for the day. It is just about 100% unpredictable. Limiting oneself at small markets is a tough way to go unless you are happy with making only booth space, after packing your vehicle setting up and tearing down.I see what you are saying about catering to a specific group, but also bear in mind that if the soaper who you send people to for non GM soaps also has GM soaps, many people will buy in as fewer places as possible.
So someone comes to your stand, wants to buy a GM soap for themselves and a non GM one for a gift. They buy the GM from you and you point them to another soaper. THAT soaper has both GM and non GM, so your customer now realises that they can go to just one booth to get the soaps that they need.
Some people will buy from two vendors anyway, because of relating to the marketing. But not all.
Don't lock yourself out of doing non GM soaps, even if it's only mentally.
I will also mention in some states and counties health regulations do not allow animals other than service animals in markets. So best to check before taking an animal with you. There are health issues and liability issues, so your market may not allow it. Where I live no markets are even allowed to let customers bring in pets, but of course the public ignores the signs