Don't forget to check GM's certified pre-owned website, though they are fewer every day. You'll get an extended warranty on the battery and two free service calls the first two years. I've really enjoyed my 2016, which is the first EV I've ever owned, and I absolutely love it.
The number one thing is to ask for a battery report. Most dealers won't do it (or simply don't know how), so don't be surprised if you don't get one.
RE: DC Fast charging. The key is to see if the charge port has an orange plastic flip-down cover on the two bottom ports. If it does, it has DC Fast charging; if it doesn't, nope. See if you can finesse the dealer into sending you a picture without letting them know that's what you're looking for. If they figure it out, it can add up to $1k to the price.
2016 Spark EV LT2, 30k miles