I have had to have liability insurance for every show I have done over the past year. It pays to ask around other stall holders for who they have their insurance with as I was originally quoted 245 GBP for my insurance but after speaking to a lovely lady at one fair I managed to get it for 39.50 GBP per year!
Part of the conditions of being accepted at one particular fair for later this year meant that I also had to complete a risk assessment about my stall and the stock I will be selling!
It's a pain, but is becoming increasingly common....