Yes, how hard one plays is subjective. There is a range of soft to hard playing that makes sense in different contexts or just for personal taste.
But no, action is not subjective because all of that could be measured. Our vocabulary about action just lacks the terms and we don't have a ready way to measure velocity.
We know how to measure relief. And we can measure the distance from the string bottom to the fret.
So what I would tell a buyer is, 'capod at the first fret, relief x, action at 12th fret is x.' Then you can best describe how heavily you tend to play (if you know, which is part of the problem, lots of new people start out with underpowered amps and are plucking like madmen to try to hear themselves) and where in usual ppp to mf or fff of that range if it buzzes at all.
But no, action is not subjective because all of that could be measured. Our vocabulary about action just lacks the terms and we don't have a ready way to measure velocity.
We know how to measure relief. And we can measure the distance from the string bottom to the fret.
So what I would tell a buyer is, 'capod at the first fret, relief x, action at 12th fret is x.' Then you can best describe how heavily you tend to play (if you know, which is part of the problem, lots of new people start out with underpowered amps and are plucking like madmen to try to hear themselves) and where in usual ppp to mf or fff of that range if it buzzes at all.