I got another uncomfortable fact to know on sd cards and different other storage types.
Available at our national TV station via stream. A regular broadcast called “Marktcheck” from Tue, 10.4. | 20.15 o’clock
Starting at minute 17.
They found out that 7/10 sd cards (other semi-conductor based storage types may as well) actually does not have the declared capacity but only 50% or even less. One of them only had 100MB but was declared having GB, “100MB” - ridiculus, where could anyone find one of such tiny capacity these days.
It affects well known manufacturers and no-name types of any kind, Samsung as well as SanDisk etc. Also no matter where they were ordered. But, the better the proposal, the higher the risk of being duped. Even the packaging looks 100% original and all were originaly sealed. Even experts could not distinguish.
It seems that storage which does not pass the final production test is being gathered and sold by scammers.
For testing the tool [H2testw] (https://h2testw.de.softonic.com/)
was used which could be used generally for any type of storage device, semiconductor based (ssd) or classic magnetical HDs.
In general it fills your storage with several 1GB files with a specific data pattern and reading/comparing them at reaching full storage afterwards for changes.
Doing this manually using another checksum algorithm should do as well, like MD5, sha…
Such test should always be done prior to use the storage for whatever purpose to prevent being scammend or not to stumble over any surprise much later after having serious data troubles or data loss.
I have tested all of mine with positive results.
They were spread from 1GB up to 128GB.
Test duration can widely vary depending on different factors such as system/OS type, speed class, connection type (USB1.1/2/3.0; respectively POI/pATA/sATA), reader type or converter type. Also I believe there is a speed limit due to the tools file operation as I always was far off from my usual transfer rates.
I can provide my time estimations for my tested cards.
Using a Delock USB3.0 single-slot sd card reader on USB 2 port 
2GHz Dual core AMD; M$-XP
AData 1GB (80x) ~ 20mins.
AData 8GB class 6 ~ 40mins.
Samsung 32GB class 10 ~ 90mins.
Samsung 128GB Evo+ U1 ~ 200mins.
Intel Core2Duo 2,5GHz Vista64
Delock USB3.0 single-slot sd card reader on USB 3 port
Samsung 128GB Pro+ U1 ~ 200mins.
It looks like I have been lucky up to now with all my storage purchases.