Actual Sideloading - this would probably cause many iPhone users to brick their device by installing malware without knowing.

If Apple allows sideloading modded apps it’s over.

The Ringke Onyx case is underrated.

I’d always try to get last year’s pro version (14 pro) used. Of course, you would need to know what to look out for when buying second hand (battery %, imei, seller reputation).