Yes, make sure it has a clean esn. Happens too often that they say clean esn, when it's not. Have the person give you the esn over email or phone, then call Verizon to make sure it's clean. Before you give the person your money, check to make sure the esn matches what he already gave you. If so, then you should be good to go.
I called Verizon with the ESN. They stated that it is clean. The seller said they switched to a non-data plan & don't need the phone. They used it for 2-3 weeks.