Ideally you will have a written and signed contract. But you may have other documentary evidence - for example, a purchase order. You will also want evidence that you fulfilled your side of the bargain (eg a signed delivery note).
It will be helpful if there is clear evidence that you made the customer aware of your terms and conditions before the contract was agreed.
Ensure, also, that you keep copies of any correspondence you send while chasing the debt or attempting to negotiate a compromise.
Even without direct evidence, it may be possible to infer the agreement from related evidence - where the customer has proceeded in a way which suggests that there is an agreement, or from the correspondence you send and receive while chasing the debt. Discuss the quality of your evidence with your solicitor before taking court action, particularly if there is a dispute over the debt (see 14 below).
