Thats the whole point. There is NO way to enforce any sort of deals in DDO, so they are not 'contracts'. They are non binding, non compellable deals that rely on the good faith of both parties. One element of a contract is that it is binding, unlike a trade in DDO. Any 'lawyer', not just this one, will tell you that.
Best way to approach it, from my experience, is to make the deal and then execute it right away. The longer the wait, the more likely it is that it will fall through somehow. And if it does fall through, there is absolutely nothing you can do about it, except be a little more cautious when dealing with the same person. Although I bet the Coin Lords would probably break his characters legs for a little plat.