First, Let me say that the spark has some great reviews (I've never seen one in person since it's only sold on the left coast), and since this is a forum dedicated to Chevy electric vehicles, I think it would be a great choice for your business, except for the problems that relate to deductions for business use.
I must, however, point out an alternative vehicle that my wife and I own. The Mitsubishi i-miev. It also has seats that fold flat creating a flat floor for cargo. Although this vehicle gets dinged for it's shorter range, our i consistently yields better range than the EPA estimate (this morning it estimated 82 miles of range when it departed the garage). This better range is a result of my wife driving it on local streets at 45-50 mph, similar to how a delivery vehicle might be driven. Another reason people turn up their nose at the Mistu, is that it has a rather plain or basic (utilitarian) interior, again no problem for a delivery vehicle. But the i-miev has the Chademo connector for DC fast charging (The spark uses the J1772 frankenplug of which there are few if any fast chargers available) and the Mitsu starts at about $22,995 compared to the Spark's $26,685 MSRP. If you're willing to go get one, there are several used i-miev's available in the 10,000-14,000 range with 10,000 miles or less. If you do consider this alternative keep in mind that all 2014's have the DC fast charging, but on the 2012's it was optional, so be careful!