How many times have you been over-promised and under-delivered…it happens daily, so if you really want to create separation, be the exception!
Getting that first order is hard, you want to make sure that you give them a reason to come back for that second order as well. Even if your business sells big one and done items like a pool or a house, you still need those referrals. Maybe a follow up with a 10% discount as a thank you? Maybe a discount for a referral? Maybe give them a coupon to hand out to friends who need your services (winner for both of them!).
Make it impossible not to refer you because you more than did what you promised!