It depends if he's actually entered a contract when suggesting the heads or tails scenario. If the Shopkeeper's legal team are present, (and I'm assuming they are), properly constructed papers should be made out and completed to satisfy UK law. Dom might walk out without honouring his side of the "bargain", but I would expect the full weight of the law to be brought down on him to reach a satisfactory conclusion, (it being satisfactory to the trader). I'd also expect the Shopkeeper to be awarded costs, and that any follow-up of inaccurate reporting of the event, be subject to the laws of the land relating to libel or slander.
