If you’re a stallholder in most cases, yes, but it’s not required as frequently by organisers. Adding products liability cover ensures you have cover for your legal liability for personal injury and property damage as described and caused by any goods, products and property (after they have ceased to be in your possession or under your control), which are deemed to have been manufactured, grown, extracted, produced, processed, constructed, assembled, erected, installed, repaired, serviced, treated, sold supplied or distributed by you including any container thereof. (Generally this does not apply to organisers unless they too are a stall holder as well.)