Whether a pair of shoes can be resoled is settled before anyone buys them. The construction method chosen in the factory determines whether a cobbler can ever separate the sole from the upper.
Cemented construction is the common case
Most shoes made today have the sole glued directly to the upper under heat and pressure. It is fast, cheap and produces a light, flexible shoe.
The bond is designed to be permanent. Removing it usually damages the upper along the edge, and the remaining material is often too thin to take a new attachment.
Some cemented shoes can be re-soled by grinding and regluing, but the result is a repair with a shorter life than the original rather than a rebuild.
Welted shoes are built to be taken apart
In a welted shoe a strip of leather is stitched to the upper and an insole rib, and the outsole is then stitched to that strip rather than to the upper itself.
Replacing the outsole means cutting only the outer row of stitching. The upper is never disturbed, which is why a welted shoe can be resoled repeatedly.
The cost of that capability is in the making. Welting requires more material, more operations and more skilled labour, all of which appear in the retail price.
Stitchdown and moccasin methods sit in between
Stitchdown construction turns the upper outward and stitches it directly to the sole, giving a repairable shoe with fewer components than a welt.
Moccasin construction wraps the upper under the foot, and a replacement sole is stitched or cemented onto that base without opening the shoe up.
Both are repairable in practice, though the number of cobblers willing to work on them is smaller, which affects the real-world cost of a repair.
Sneakers are a special problem
Athletic shoes typically combine a cemented outsole with a moulded foam midsole. The midsole compresses with use and is the part that actually wears out.
Replacing a foam midsole is not a repair operation. There is no standard part, the bonding is industrial, and no cobbler is set up to remould it.
Which is why sneaker restoration focuses on cleaning, repainting and replacing laces and insoles, none of which restores the cushioning that has gone.
What this means at the point of purchase
The stitching visible around the edge of a sole is the clearest signal, though decorative fake stitching is common enough to be worth checking closely.
A shoe that can be resoled three times has a very different cost over its life than one that cannot, even at several times the purchase price.
The calculation only works if the upper survives that long, which puts leather quality and regular conditioning at the centre of whether repairability pays off.