The first thing I check on a dining set is whether the table and chairs actually came from the same design conversation, or if someone just boxed up a table and grabbed chairs that were cheap to ship alongside it. You can tell. The wood tone is slightly off, the leg shape doesn't echo anything, the proportions feel like a compromise. A set that was designed together has a rhythm to it, the chair rail height matches the table apron, the finish on the legs matches the tabletop under the same light. That rhythm is the whole point of buying a set instead of mixing pieces yourself.
Where sets fall short is flexibility. You get what you get, six chairs that all match, a table sized for exactly that many, and if your household changes or you want to mix in a bench or a couple of mismatched end chairs for character, you're fighting the set's own logic to do it. If you like a room that looks collected over time rather than delivered on a truck, a set can feel stiff. I'd also skip a set if your dining area is oddly shaped or doubles as a desk or craft table, because sets are built for one use and don't flex the way separate pieces can. The day it arrives, check that every chair sits level on the floor with no rock, check the table leaf or extension mechanism if there is one, because a lot of extending tables develop a gap or a wobble at the seam within the first year if the hardware's cheap, and run a hand along the underside of the table for rough spots or staples poking through, especially on anything upholstered.
How it ages depends almost entirely on material, and this is where I've learned the hard way. Solid wood, oak or acacia, takes scratches and dents as character and can be sanded and refinished down the line, which matters because dining tables get used hard, homework, wine glasses, someone's elbow every single night. Veneer over particleboard looks identical on day one and then chips at the corners within a couple of years, and once it chips there's no fixing it, only covering it with a runner. Upholstered chairs in a performance fabric wipe clean, in real linen they stain the first time a kid spills juice, ask me how I know. Wipe spills immediately, use coasters under hot dishes even on a sealed finish, and tighten chair screws twice a year because the wobble always starts there first.
A set like this suits a household that eats together often enough to want everything to match and nobody arguing over which chair is theirs.