I've quit taking my body butters and sugar scrubs to markets for just that reason - they melt. I'm now reserving those for indoor markets, home parties and the mall..... Right now I won't even ship a body butter, lip balm, solid lotion stick, or anything else similar for just that reason. I've let my customers know that if they do want to order that - to do so in the fall once the temps drop so it will get them in a non-liquid state.
If you only do summer outdoor markets you could put them in a cooler and have a mocked up jar to show that the product is in your line-up and then pull out your sample and selling ones out of the cooler. Just make sure they know that they really need to keep this cool because it will melt in extreme heat....