Well it's a truck bed. Only way to have no wear and tear on it is to not use it.
I'm pretty anal about keeping things looking nice but the truck bed does not make that list.
Drop in liners will wear the paint off. Spray in liners will fade, dent and get tore up if you're using the truck.
Suggestion is to get a cheap tonneau for the back with whatever option you choose. Takes only seconds to fold up or remove. Keeps rain, dirt, leaves etc out of the bed. Will keep bed liner from fading if you don't need an open bed all the time. Visual and weather protection for day to day stuff in the bed and hides scratches from plain view.
I don't believe a scratched or dinged up truck bed detracts from resale on an older otherwise clean truck. It's expected. And most people buying an old used pickup are going to use it as a pickup, not a show car.