Before you enter into any business agreement with anyone, let there be documentation of contractual agreement. The business life is not that of sentiments. The mutual trust that is build in business if it is to continue should be documented.
In business why should you agreed to a verbal agreement? Do not be desperate in entering into a business deal without drawing out the contractual terms, condition and the profit sharing formula. Business is business and friendship is friendship; let no sentiment be found on this.
Many people who have gotten their hands burned in business deals are as a result of no contractual agreement. Remember the law has no excuse for ignorance. Though business is build on mutual trust, but there need to be some written agreement to help define the term of contract agreement which is for the benefit of all parties concern.