Pre-owned phones from Sprint have 90 day limited replacement warranty (Effective January 13, 2017).

Pre-Owned 90 Day Limited Replacement Warranty provides replacement coverage for eligible pre-owned phones due to mechanical or electrical failure, with valid warranty claim and phone return via claim shipping process. Please note that return shipping of your pre-owned phone is at your expense. The Replacement pre-owned phone may be different brand, model, and/or color or contain non-original manufacturer parts. The 90 Day Limited Replacement Warranty is not an insurance policy and does NOT cover lost or stolen devices, normal wear and tear, or damage from accident or abuse.  source