To help you on your journey into the world of pre-loved cameras these are some of the reference sites I’ve found incredibly useful. Use these for technical and market information alongside my own unscientific reviews of cameras and buying guides
Reference
Camera Wiki: https://camera-wiki.org/
Camerapedia: https://camerapedia.fandom.com/
CollectiBlend: https://collectiblend.com/Cameras/
The LensDB: https://thelensdb.com/
Camera Manual Library: https://butkus.org/chinon/index.html
Ebay Advanced Search: https://www.ebay.co.uk/sch/ebayadvsearch