Once approved, the pre-production sample becomes the reference the whole order is inspected against. Everything you do not check now is something you have implicitly accepted.
Check it packed, not empty
This is the single most useful rule. An empty pouch cannot tell you whether the contents fit, whether the closure still works when full, whether the flap lies flat when loaded, or how the pouch presents on a counter with the product in it.
Put your actual product inside. Not a similar product — the real one, in the state it ships in.
Fit and closure
With the product inside: does the closure work without strain, does a drawstring still gather cleanly, does a flap lie flat, does a zip run without catching on the contents. Then take the product out and put it back several times — retention and removal are two different tests and buyers usually only do the first.
Fabric and colour
Check colour under the lighting the product will sell in, not office light. For pile fabrics, check with the nap running the direction production will use. Check the inner face against your product for marking, especially with polished metal, lenses or soft finishes.
Decoration
Check position relative to seams, squareness, coverage across solid areas, and the finest element in the design. Rub it firmly to test durability. Confirm the colour of foil or print on this fabric rather than on a swatch.
Construction
Look at stitch density and straightness, seam allowance, any exposed raw edges, and how the corners are finished. Turn it inside out — inside finishing is where corners get cut, and it is what customers see when they use the pouch.
Keep a counter-sample
Keep one approved sample yourself, sealed and dated, and confirm the factory holds a matching one. If a dispute happens later, the physical counter-sample is what resolves it. Photos of an approved sample are much weaker evidence than the sample itself.
Write down what you approved
Approve in writing and be specific about what the approval covers: fabric, colour reference, dimensions, closure, decoration method and position, packing. "Sample approved" is ambiguous. "Sample approved: fabric and colour as sample, foil position as sample, internal dimensions to be confirmed at X" is not.
If something is wrong
Ask for a revised sample rather than approving conditionally. A conditional approval — "fine, just move the logo up 5mm" — relies on that instruction surviving into production. A second sample costs a few days and removes the ambiguity entirely.