How do you tell a good tag from a bad one before buying?
Not from the photograph and not from the price. Three things separate them: what the listing is willing to state, what a sample actually measures, and what survives a week on the real surface. A supplier who will not answer the first is telling you about the other two.
What a good listing states
The chip reference, by name. The NFC Forum tag type. The usable free space, as distinct from the total memory. The substrate. The adhesive, and the surfaces it is meant for.
None of that is commercially sensitive and all of it is known to whoever made the tag. A listing omitting all five is not protecting a secret, it is passing on what a trader was told.
The single most revealing omission is the tag type. It is the property that decides whether phones read the tag at all, and its absence is the strongest signal available.
What a sample tells you
Read one and compare what the tool reports against what the listing claimed. The chip, the tag type and the free space are all reported in seconds.
A mismatch is decisive. A tag sold as one chip and reporting another is not a quality question, it is a different product.
Then read it with the oldest phone you can find, in a case, held the way a stranger would. That is the working condition, and a tag that needs a practised gesture will disappoint in public.
The week long test
Stick a sample to the actual surface, in the actual place, and leave it.
Most physical failures announce themselves within days: corners lifting, the adhesive not wetting the surface, moisture at the edges, a substrate that curls. A week costs nothing and answers what no datasheet can.
Handle it daily if the deployment involves handling. A tag that reads perfectly and fails after fifty touches is a tag you want to discover before ordering a thousand.
Signals that cost nothing to check
Consistency across the sample. Ten tags from one batch should report the same chip, the same free space and similar behaviour. Variation within a batch predicts variation across an order.
Whether the supplier will name the manufacturer. Traders who cannot are several steps from the factory, and each step is a place a substitution can happen.
Whether they answer a technical question with a technical answer. "NFC compatible" in response to a question about tag type is an answer about the supplier.
And whether the same product keeps the same specification over time. Reordering and receiving something different is the failure this whole exercise exists to prevent.
Frequently asked questions
Does a higher price mean a better tag?
Not reliably. Price tracks form factor, features and order quantity more than quality, and a cheap compliant tag outperforms an expensive unsuitable one.
Can I judge quality from the packaging?
Barely. Packaging is chosen by whoever sells the tag rather than whoever made it, so it says little about the inlay inside.
How many samples should I order?
Ten is enough to see batch consistency and to run a physical test. It costs almost nothing against the risk it removes.
What if the supplier will not send samples?
Treat that as an answer. A supplier confident in their product sends ten tags without difficulty.