I don't know enough (anything actually) about sale of goods where goods are substantially altered (grated) prior to being paid for. This, I presume is going to be the basis of your client's action. I don't think an argument on whether there is a contract or not is going to be particularly fruitful unless you can come up with case law on this kind of thing. Does the custome create an implicit agreement etc.
I personally think you could be advising your client to seek an equitable remedy - that your client relied upon the promise to purchase; and cut and weighed the goods to their detriment, and the customer should be estopped from withdrawing the promise to pay.