On counterfeit SD cards
F3 is the best, quick and easy
sudo f3probe --destructive --time-ops /dev/sdb
easy peasy, on most auction sites that is all it takes is to report a counterfeit and get your money back.
That said for all but the gobs of 8gb I buy for embedded stuff I try to buy from real stores where fakes in the supply chain would be difficult.
In my own experience :  The only time I have had a problem using a micro-sd card,  it has turned out to be the card reader that was defective.
  *  ( or I did something wrong Confused )

While I have only been using micro-sd cards for the last 2 or 3 years,  I have purchased 35-40 cards at places such as :  
         New Egg, and various Ebay sellers, ...  and,

I do stick mostly to brands I recognize,   and I do always use  class 10....

Note : I have not ever got an sd-card that was a different size than what I bought, but the largest so far has only been 64gb

  I only see very slight differences in how they actually  'run in real time use'  in my Pine64 products.

  *  What speeds they do actually run in my devices is more important to me, than what a fancy test score shows.

 Example :
 If your device has a read speed limit of 80 mb/s,
   Then, a card that says it reads 180 mb/s is not going to improve your real time performance.

*  I do have quite a collection of micro-sd card adapter/readers,    THAT is where I do see a huge difference in performance.

Your experiences may be different.
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In my experience from a few years ago you could f3probe /dev/sdc and get a read if the card/or other flash is fake.
A few years ago the big auction site most sellers of fake flash would do a quick refund for all memory that came up fake to keep their store open and ratings good.
I personally only buy from big stores with established supply chains and very carefully inspect the packaging for flash media and batteries as both are quite available commodities around the world and also frequently counterfeited.
In any case have your receipt in hand, buy form established corporate retailers who would rather have a relationship with a flash vendor like sandisk and also have the deep pockets to fear lawsuits for selling counterfeits, and f3probe your media when you get home to be sure.
I only use Asian discount and auction sites for 8GB and below sized cheap flash memory for embedded stuff or as give away full of data or media like floppy disks of old.
I have good experience purchasing Lexar memory cards and flash drives, regardless of where I (or those I recommended these to) had purchased them, I have yet to see a single fake (whether this is AliExpress, eBay, Amazon US, Mymemory.co.uk, WalMart, etc.), and I had started purchasing them around a decade ago (back when they had belonged to Micron, now they belong to Longsys, however for the most part, their quality hasn't dropped too much).

For anyone wondering, their flash drives and memory cards almost exclusively (if not exclusively) rely on flash storage from Micron (even now).

I also have good experience with their performance and longevity, especially at their price brackets.
Counterfeits seem to come in waves but I have only ever received one where a 32gb really was 8gb and doing that write over thing.
That was maybe 2 years ago now maybe longer when 32gb was considered a large card.
I have a hunch its the larger newer, faster cards that only have a revenue to make it worth while and same as above from various sources its been a while since I hit a dud.

There are so many x3 packs where my usual maker 32gb I can get A1's for £4 each and at that price I have doubt if its worth the counterfeiters and sellers time.

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