What the service name covers, and what it does not
Quality assurance, as a service name, means that a maker checks its products before they are shipped. It does not, on its own, define what is checked, how it is checked, what counts as a defect, or what happens if a defect is found. Those details are the actual quality arrangement, and they should be agreed for the order in question rather than assumed from the service name.
This site therefore presents quality assurance as a set of questions: what is inspected, at what stage, against what standard, and with what remedy. A buyer who needs a particular inspection or a particular remedy should state it in the inquiry and ask for a written confirmation.
What to ask about inspection
Ask what is inspected before shipment: the design, the colours, the stitching, the closure, the labels and the packaging are all candidates, and the inspection may cover all of them or only some. Ask whether inspection covers every cap or a sample of the batch, and ask what happens to caps that fail inspection.
For a first order, ask whether the sample inspection and the batch inspection use the same criteria. A sample approved against one set of criteria and a batch inspected against another is a recipe for disagreement, and aligning the criteria before production is a simple step that prevents it.
What to check on delivery
On delivery, check the caps against the approved sample and the written brief: style, logo position and size, colours, closure, labels and packaging. Note any difference promptly and in writing, with photographs if possible, because a quality claim made promptly with evidence is far easier to resolve than one made later without it.
Keep the sample, the written brief and the delivery photographs together. That set of records is what lets a quality question be answered on evidence rather than on memory, and it protects both the buyer and the maker.