There is an old adage that a wise engineer once told me; Always, always get everything in writing. Getting things in writing would make everyone’s life easier… But only if the person who prepared that document is ready to devote the required resources. I once had a manager promise the world, but then when I asked if I could get it in writing, reality set in. An oral agreement is much harder to defend. It is a lot of he said/she said. It is much better to start with a written contract establishing the business relationship and terms.