Here is my experience about how to tell oem iPhone screens or not.

1. Resolution Quality: Compare the new screen to an original one. Check if the resolution is as high and clear.

2. Flex Cable Markings: Check to see if there’s a “V” print and Apple logo on the screen flex cable ribbon. If not, possibly that’s a fake one.

3. LCD Flex Cable IC Chip: There is a chip on the LCD flex cable that regulates power and display information from the main board to the LCD itself.