Typically the only used ebikes available are "used up" ebikes, or cheaper chinese models that would not fit your purpose. Also their batteries arent that great and age has made them worse.
I havent been impressed with Giant or Trek offerings when I have ridden them in the past.
With your delivery idea, think about a class 3 bike. A I or II would give you longer range but a 3 can get you there faster.
One of my customers is using a BH Rebel Cross. The Yamaha drive works great and can still be pedaled when you run out of power.
-SP