A good chair holds you without you noticing it's doing anything at all. You sit down, your weight settles somewhere around the hips and lower back, and that's it, no shifting every ten minutes, no numb spot creeping in halfway through dinner. A bad one announces itself within a minute, usually in your tailbone.
The difference between a chair that lasts and one that starts wobbling by its second winter comes down to things you can't always see from across a showroom floor. Flip it over before anything else. Dowel joints that are glued and pinned, not just glued, hold up to being dragged across a kitchen floor a few thousand times. A frame that's solid wood, or at least a good plywood, will take a toddler standing on it in a way particleboard never will. Leather that's actually tanned hide and not a printed vinyl will soften and age instead of cracking at the seams in a year. And the finish matters more than people expect, a thin coat that wears through to bare wood at the arms within a season tells you everything about what corners got cut elsewhere. Run your hand along a joint, press down on the seat, give the back legs a little shake. If anything creaks or gives at this stage, it's not getting more solid with age.
Where a chair belongs depends entirely on what you're asking it to do. A dining chair needs to survive getting pulled out and pushed in several times a day without the joints loosening, which rules out anything too delicate no matter how good it looks in a rental listing. An accent chair in a living room gets to be a little more precious, since nobody's climbing in and out of it with wet boots, but it still needs to earn its square footage, because one oversized chair in a small room will eat the walking path between the sofa and the door faster than you'd think. A chair that works beautifully in a spare bedroom corner might be exactly wrong crowded next to a coffee table where everyone's knees end up touching.
In an ordinary room, a chair sits well next to things that give it a little breathing space, a side table at arm height for a coffee cup, a lamp if the room goes dark early, nothing stacked right up against it. Leave at least a couple feet to walk around it, or it stops being a chair and starts being an obstacle.
When you're looking at one, check the joints and the underside first, before you ever sit down.