I signed a contract with Verizon for the 6s, but then bought out the phone to go back to Android. I would like to sell the iPhone now. Do I need to remove a SIM card? Since I bought the phone outright (paid it off), is it unlocked? Is there anything I need to be concerned about before selling privately?
I would remove the SIM card. The new owner can easily get one for their plan. You will need to make sure you remove the iPhone from your Apple ID in addition to erasing it (erasing it alone won't remove it from your iCloud/Apple ID). It is unlocked but when you list it for sell (if you're actually listing it somewhere like eBay) you need to disclose that it is a Verizon iPhone. The model number is different for the truly unlocked sim-free version you can buy from Apple but for all intents and purposes your iPhone is unlocked.