Drive around Raleigh, Cary or Apex and you can spot them from the road: retaining walls with a belly in the middle, caps that have parted company at a joint, a top course that has walked forward two inches. The stone looks fine. The wall is failing anyway.
Almost every one of those is a water problem. Piedmont clay does two things that make it hard on walls. It holds water instead of letting it pass, and when it is saturated it pushes — hard. A four-foot wall holding back a wet clay bank is carrying far more load than the same wall holding back dry sandy soil, and it is carrying that load with nowhere for the water to escape.
A wall that holds has four things behind it that you never see once it is finished. A trench dug down to firm ground, not to the first depth that looked convenient. A compacted stone base, set so the first course is dead level, because every error in that first course is multiplied by the time you reach the top. A column of washed stone against the back of the wall, wrapped in filter fabric so clay fines cannot migrate in and plug it. And a perforated drain line at the bottom of that stone, sloped, with an outlet that actually daylights somewhere sensible instead of stopping six feet in.
That is also where the cheap quotes save their money. Backfilling with the same clay you just dug out costs nothing and looks identical on day one. Skipping the fabric saves an afternoon. Running drain pipe to nowhere is faster than finding a fall across the yard. None of it shows up in a photo, and all of it shows up in three winters.
When you compare quotes on a wall, ignore the stone for a minute and read the line items underneath. How deep is the excavation? What is the backfill material? Is there filter fabric? Is there a drain line, and where does it come out? Is there geogrid if the wall is tall or has a driveway sitting above it? If a quote does not mention any of that, it is not a cheaper wall — it is a different, shorter-lived product.