I learned this from a tailor who was tired of me asking whether things were worth the money. She turned a jacket inside out on the counter and pointed at four things, and I have used the same check ever since.
Seam allowances
The fabric beyond the stitch line. It costs money and it does nothing visible, which is exactly why it gets cut.
Generous allowances mean the garment can be let out or taken in later, and they mean the seams will not fray apart.
A quarter inch of allowance overlocked tight against the stitch line means the garment is finished, permanently, at that size.
This is the single clearest indicator of what a manufacturer was willing to spend, and nobody photographs it.
Pattern matching at the seams
Where a stripe or check crosses a seam, do the lines continue?
Matching patterns requires cutting each piece in a specific position, which wastes fabric — sometimes a lot of it.
Which makes matching genuinely expensive, and it is why cheap checked shirts have lines that jump at every seam.
Look at the front placket, the pocket, and where the sleeve meets the body. Those three tell you most of it.
The interfacing question
Inside collars, cuffs and jacket fronts, something stiffens the fabric.
Fused interfacing is glued on, which is fast, cheap, and eventually bubbles and separates after enough washing.
Sewn-in canvas is stitched, which is slow, expensive, and moves with the fabric rather than fighting it.
You can feel the difference by pinching the fabric layers between finger and thumb — fused feels like one board, canvas has a slight independent float between layers.
On a jacket this is the difference between something that hangs well for a decade and something that looks tired in two years.
Buttons and how they are attached
Plastic buttons that feel light and warm are polyester. Shell buttons feel cold and heavy and have visible irregular grain. Horn buttons are warm but dense and each is slightly different.
None of this determines whether a garment is good, and it correlates strongly with what else was spent.
More useful is how they are sewn. A shank — a small stack of thread between button and fabric — lets the button sit properly over a layer of cloth. A button flat against the fabric on a thick garment will strain and pull.
The lining
Cheap linings are thin polyester that does not breathe, which is why some jackets are unbearable in any warmth.
Viscose or cupro lining breathes considerably better and costs more.
Also check whether the lining is attached loosely with a pleat at the back. That pleat is there so the lining can move when you reach forward. Without it, the lining tears first, usually at the armhole.
Fabric weight tells you about drape
Pick the garment up. The weight in your hand is information.
Lightweight fabric in something structured — a blazer, a coat — will not hold shape, regardless of cut.
Heavy fabric in something meant to flow will hang like a curtain.
This is not about better or worse, it is about whether the fabric matches what the garment is trying to do, and the mismatch is common in fast production because fabric is sourced on price rather than on suitability.
What I have stopped caring about
Brand, mostly. Price above a certain point, mostly.
Both correlate with construction quality very loosely, and the correlation has weakened as luxury groups have moved production and cut costs while raising prices.
The inside of the garment does not lie about any of this, and it is available to look at for free before buying.
One caveat
Good construction on a garment that does not fit you is worthless.
Fit first, construction second. A well-made thing in the wrong shape stays in the wardrobe, and I have several proving the point.
But between two things that fit, this check reliably tells you which will still look right in five years.
Seam finishing types
Worth knowing because it tells you what happens after a few dozen washes.
An overlocked edge — the thread wrapping around a raw cut — is the fast standard and it holds fine on most things.
A French seam encloses the raw edge inside a second seam, so nothing frays and nothing is visible from either side. It uses more fabric and more time, and it appears on shirts where somebody cared.
A flat-felled seam folds both edges under and stitches twice, producing the double row of stitching on jeans and workwear. It is the strongest of the three.
Bound seams wrap the edge in a separate strip of fabric, which is the most expensive and appears mostly on unlined jackets where the inside is visible.
The thread itself
Rarely discussed and it fails often.
Polyester thread is stronger than cotton and stretches slightly, which means it survives movement. Cotton thread on a stretch fabric snaps.
Stitch density is visible — count the stitches over an inch. Sparse stitching on a stress seam is where a garment will open first, and it is the cheapest possible saving to make.