If it is a fake iPhone with a "correct" serial number then it will not run iOS and it will not have a functional Touch ID. And the fake serial number is unlikely to match the phone you are looking at.
Hi
Apple's instructions for identifying an iPhone by its model number and other details are provided here:
Identify your iPhone model - Apple Support
To also check the service and support coverage for an iPhone, enter the serial number here:
How do I facetime someone if I'm just about to buy the?
Some fake phones have the correct serial numbers
Buy only from a reputable source.
Determine Fake vs. Real Iphone - VisiHow
Try facetiming another iPhone. If it works....it's the real thing.
If you are in doubt as to the authenticity of the iPhone being offered
for sale, walk away from the deal and make your purchase directly
from Apple or Apple authorized iPhone retailer.
How do I know an iPhone is original or fake?
