The first thing I check is the chain, not the letters. A name necklace lives or dies on the bit you don't notice, because if the chain is flimsy you'll be forever turning it round from the back of your neck where it's crept over the course of a day. I want some actual weight to it, not so much that it drags on you, but enough that it sits flat and doesn't swing about and catch on everything. The letters matter too, obviously, but a lot of the cheaper ones are so thin they bend if you so much as lean on a table wrong, and once a name plate is bent it never quite sits straight again.
In the shop, or online with the zoom in, look at how the name is actually attached to the chain. Some are soldered on properly, some are just looped through a tiny jump ring that will eventually wear thin and let go, usually at a moment with no warning and no chance of finding the thing again. Check the clasp too, a lobster clasp you can do up one handed is worth more than people admit, because doing up a necklace behind your own neck every morning is not a skill most of us have. Gold plated over a base metal will wear at the edges first, especially where it sits against your collarbone or rubs on a scarf, so look closely at the plating round the letters themselves, that's where it thins fastest. Sterling silver with a gold vermeil finish tends to hold its colour longer than plain plating over brass, and it's usually worth the small jump in price for that alone.
Over months, a lot comes down to how you treat it rather than what it's made of. Perfume and the chlorine in a swimming pool are the two things that age plated metal fastest, so I take mine off before either. Store it flat or hanging rather than balled up in a drawer, because fine chains tangle into a state that takes real patience to undo, and pulling at a knot is how you snap the thing in the first place. A soft cloth wipe after a few wears keeps it looking newer for longer than anything fancier. Worn against a plain T-shirt or a crew neck jumper it does most of the talking, which is really the whole point of it, a small personal detail rather than a big statement.
The mistake is buying the cheapest version because it's only a name on a chain. The chain is doing all the work, and the chain is exactly where the cheap ones let you down first.