The sale is made before you give the details.

That can be as simple as telling them (with a smile), "If I tell you that, you'll shop my quote to my competitors, just like I would if I were in your shoes". Before it comes down to that exactitude, you have to have a commitment in place, unless you are absolutely sure that you can provide something bigger/better/cheaper than any competitor AND have convinced your sale that this is the case.

Sorry to tell you, but you've already lost this sale, in all probability.

KS