@simona
Advice may vary a lot depending on your budget.
If buying second hand in person it's very worthwhile to display a 100% white image full screen and look for variation in the colour and brightness.
Lots of screens age poorly. Maybe the backlights age unevenly? I'm not sure.
My Dell UP3216Q is/was a good screen with good colour resolution and gamut, but it is no longer consistent in colour and contrast across its width. (It's over 10 years old though)
It's annoying and sad as you shouldn't have to replace a quality screen every 5 years.
I generally look for wide gamut and high viewing angles (eg IPS screens) but a new consumer level IPS screen can be more consistent and practical to use than an aged semi-pro screen.