I have a iPhone 7 in my possession, possibly lost or stolen. I do not want to turn it in to authorities because I don't trust their handling it.. Can you help please?

If you have found a device, turn it on and see if there's a message. The owner may have done this:

Use the Find My app to locate a missing device or item - https://support.apple.com/HT210515

"What happens if you activate Mark As Lost

...You can also display a custom message with your phone number on the Lock screen, and keep track of your device's location."

For some iPhones --> Return a lost, locked iPhone, click here --> https://support.apple.com/HT211231

Otherwise turn it into authorities responsible for dealing with lost items.