The DIY approach does, of course, exist. The problems with it are (a) there are important issues that you will fail to consider and (b) some of what you write will expressed incorrectly, perhaps to your detriment.
You should retain an experienced business lawyer to help you. Although you will need to spend some money, you probably will be able to adapt the form of agreement that you receive for use with future deals.
This information does not constitute legal advice and does not establish an attorney-client relationship.
Do it yourself methods are generally ill advised because of potential pit falls in preparing and executing documents that have not been executed by an attorney. It may be worth spending a few hundred dollars to consult with an attorney about the concerns and issues you have relating to any service agreements. Good luck.
how to take with the other gentleman have stated one step further. Do It Yourself way of handling a legal issue especially one like this is destined to fail.
Any litigation attorney will tell you that the do-it-yourself methods often turn out to be full of mistakes and ommissions, and can be useless or even harmful. Probably the main benefit of a contract is that you can later enforce it in court, for example to get paid or enforce a license or other intellectual property rights. Since this is a start-up with a valuable business idea and presumably a valuable potential deal, do have it reviewed and invest in a set of agreements with a business attorney. Any emerging business is well advised to have legal counsel available on as needed basis just for such occasions.
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Money spent up front on an attorney may save you time, money, and headache in the future, especially if (and when) the relationship ends, regardless of how or why it ends. Furthermore, to the extent the other side (there are sides to every deal) has an attorney, that attorney has a fiduciary duty to look out for his client's interest which may come at your expense, unwittingly. Finally, a good business attorney should be able to protect your interest without causing ripples in your ongoing business relationship.