A memory card reports 512GB. It formats, it mounts, it accepts files. Some time later, photographs from the middle of a trip will not open, and the ones from the end are gone entirely.
The card contains a fraction of the flash it claims. Its controller is programmed to report the larger figure, and writes beyond the real capacity go nowhere or overwrite earlier data.
What changed in 2026
- Capacities kept climbing. Higher advertised capacities gave counterfeits more room to exaggerate.
- Marketplace enforcement stayed uneven. Counterfeits persisted on large platforms despite policies.
- Video bitrates rose. Higher-resolution recording made genuine sustained write speed matter more.
- Testing tools stayed available. Free verification utilities remained the reliable defence.
How the fraud works
The card's controller reports a capacity far above the actual flash. The operating system trusts it and formats accordingly.
Writes within the real capacity work normally. Beyond it, behaviour varies: some cards discard writes silently, some wrap around and overwrite earlier data, some return errors only on read.
In every variant, the writes appear to succeed. The file manager shows the files, the sizes look right, and nothing indicates a problem until something reads the data back.
That is why the failure is usually discovered after the photographs are taken and the card has been reused several times.
Test every new card
The only reliable check, and it takes one session.
Write real data across the full capacity, then verify it reads back correctly. Tools exist for exactly this on every platform — they fill the card with a known pattern and read it back, reporting where verification fails.
A genuine card verifies completely. A counterfeit fails past its real capacity, and the tool reports precisely where.
Do this immediately on purchase, while a return is straightforward. Testing when you next need the card is testing after it has already cost you something.
Note the real speed while testing. The tools report write throughput, which is the other thing counterfeits misrepresent.
For USB drives the same test and the same reasoning apply — see USB flash endurance.
Speed markings lie too
The second form of misrepresentation, and it matters for video.
Cards carry markings indicating minimum sustained write speed — the various speed class symbols. Video recording at high bitrates requires the card to sustain a minimum rate continuously; falling below it causes dropped frames or a stopped recording.
Counterfeit and low-grade cards frequently carry markings they cannot meet. A card marked for high sustained performance that actually manages a fraction of it will fail during recording rather than at purchase.
The sustained figure matters, not the peak. Many cards achieve a high burst speed into a cache and then fall off dramatically, which is fine for photographs and not for continuous video.
Testing reveals this, which is another reason to test before relying on a card.
Buying without the risk
| Source |
Risk |
| Manufacturer directly |
Lowest |
| Established retailer, sold and shipped by them |
Low |
| Marketplace, third-party seller |
Elevated |
| Marketplace, "fulfilled by" with commingled stock |
Elevated |
| Auction sites and unknown sellers |
High |
| Unusually cheap for the capacity |
Assume counterfeit |
Price is the clearest signal. Flash has a market rate, and a card far below it for its stated capacity is not a bargain — nobody sells genuine flash below cost.
Commingled inventory is a subtler risk: on some platforms, stock from multiple sellers is pooled, so ordering from a reputable seller can still deliver a counterfeit that another seller supplied.
Common mistakes
- Trusting reported capacity. It is what the fraud fabricates.
- Testing later. Return windows close and data is already lost.
- Buying on price. Below market rate means counterfeit.
- Trusting speed markings. Frequently fabricated.
- Assuming a brand name on the card means anything. Packaging is easy to copy.
- Only writing a few files to test. Passes within the real capacity.
- Reusing an untested card for irreplaceable work. The expensive version.
FAQ
How do I test a card?
Use a full write-and-verify utility rather than copying a few files. Free tools exist for every platform; the test takes as long as writing the full capacity, so plan for a while on large cards.
What if a card fails the test?
Return it and report the seller. Keep the test output, which is clear evidence of misrepresented capacity.
Can a counterfeit be reformatted to its real capacity?
Sometimes, with specialist tools, and the underlying flash is usually poor quality too. Not worth relying on for anything important.
Do genuine cards ever fail this test?
A genuine card should verify completely. A failure indicates either counterfeiting or a genuinely defective card, and both warrant a return.
Where to go next
For flash reliability over time, read USB flash endurance. For storage decisions on phones, phone storage tiers, and for keeping data safe generally, NAS backup strategy.