I should set this post to re-publish every month as every week I get a call from a newsagent with an issue about a supplier that would be resolved if there was a signed contract documenting all obligations.
This week I have had calls about a newsagency software company and a shop fitter. Last week it was a landlord situation for which there was no signed lease. Earlier this month it was about a supplier who promised goods were sale or return but did not back this with a written contract.
If you agree terms with any party on any matter, document it and have the agreeing parties sign it. Anyone refusing to document anything they have agreed to is not actually agreeing anything with you.
It is that simple.