How gutters actually fail here
Afternoon thunderstorms through the summer can drop a heavy amount of rain in a short window, and a gutter that is undersized or pitched wrong overflows straight down the fascia rather than into the downspout. Over a season or two that overflow rots the fascia board and can push water back toward the roof edge.
Salt laden air also speeds up corrosion on cheaper gutter hangers and screws, so a gutter that looks fine can be barely hanging on where the fasteners have failed underneath.
Sizing and pitch
A standard five inch gutter is enough for most roof sections in this area, but a larger roof plane or a valley that concentrates a lot of water often calls for a wider gutter and a larger downspout to keep up during a heavy storm. Pitch is checked with a level over the full run rather than eyeballed, since a quarter inch of drop over the wrong distance leaves standing water that attracts mosquitoes and adds weight the hangers were not sized for.
Repair versus replacement
Sagging sections, separated seams and a handful of loose hangers are usually a repair. A gutter system that is undersized for the roof it serves, or one with corrosion through the metal in multiple spots, is a replacement, and that gets explained plainly rather than patched repeatedly on repeat visits.
Downspouts get extended away from the foundation where the ground allows, since water dumped right at the base of the house is one of the more common causes of a wet crawl space in this area.
Gutter guards and leaf load
Homes shaded by live oaks or pines around Wilmington deal with a heavier leaf and needle load than an open lot in a newer subdivision, and that debris is what clogs a gutter fastest. Guards help, but the wrong style traps pine needles just as easily as it keeps out leaves, so the choice depends on what is actually falling on the roof rather than a one size fits all product.
A gutter that overflows in a heavy thunderstorm is not always a sizing problem. Sometimes the run is simply full of debris that never got cleared after the last storm, and clearing it is the whole fix.
Fasteners near salt water
Gutter hangers close to the beach towns corrode faster than the gutter material itself in a lot of cases, which is why a gutter that looks structurally sound can still be barely attached to the fascia. Stainless hardware costs more up front and holds considerably longer in that environment, and it gets used as the default on any gutter job within a mile or two of the water.