Same day delivery isn't a USP, there are plenty of couriers, men with vans, etc that any of your competitors could use to get their products delivered urgently. If they don't do it, its because there isn't the demand or they haven't realised. If there's no demand, then you don't have a USP, if there is a demand they can copy you in 2 or 3 phone calls. The same applies to stock, if you can hold all that's needed with £14k of stock, so can they. And £14k is a lot less to them.