How can I know my iPhone is original?

Settings > General > About > Model Number

The first letter in the model number represents the source of the device. Currently, there are four known possible choices:

• "F": refurbished unit
• "M": retail unit
• "N": replacement unit
• "P": personalized (engraved) unit

Why do you believe it is not original?

Why do you believe it is refurbished?