Note that you don't often see an explicit transaction definition for a transaction like this; the definition is encoded in the people, processes, and technology that you interact with. For low-consequence transactions such as Daisy's, the transaction definition is implicit. Only if there's a dispute do we get to find out how the transaction is defined. For example, if Daisy's bicycle chain snaps after a couple of days, she might reasonably expect that the chain would be fixed free of charge, or the bicycle replaced, or she would get her money back. This is the point at which Daisy determines the true nature of her transaction with the Winchester bicycle shop.

It looks like this kind of implicit transaction definition only has downsides—but in fact that's not the case. Firstly, every country's laws have explicit notions of a fair transaction that would give Daisy reasonable expectations as she entered the transaction. In most countries this is called something such as a Sale of Goods Act, and it specifies the rights and responsibilities of all counter-parties involved in any commercial transaction. Secondly, the lack of an explicit contract simplifies the interaction between Daisy and the bicycle shop. Given that, in most cases, bicycles perform well for an extended period after purchase, a receipt is sufficient for most practical purposes. It would be both costly and timely to re-state what everyone knows to be true every time a simple purchase was made. This kind of simplification is an example of what people often call reducing friction.

For high-consequence transactions, or those with special conditions, the situation is very different—it is vital that the transaction definition is made explicit, in advance. If we look at Daisy's transaction again, we can see that if there was a dispute, there would have been other follow-up transactions—for example, the bicycle might have had its chain replaced, or in an extreme circumstance she might have got her money back. We can see that, in general, we would require several conditional transactions to describe a satisfactory interaction between participants for such a transaction. It means that if Daisy had been getting a mortgage, rather than a bicycle, it would have been necessary to specify several transactions and the conditions under which they could be executed. You've probably heard of a term for such a collection of transactions and conditions—a contract.