I just received a 128GB MicroSD card off Amazon, as I type this I’m verifying that it is what it claims to be, an actual 128GB of thumbnail-sized storage. The sad reality is you can trust no vendor regardless of how reputable, brick and mortar or online, because anywhere in the supply chain counterfeits could crop up. The fakes typically have a smaller amount of storage than listed and falsely display the desired size to your computer or device, but in reality once the volume is full your data gets overwritten and is unrecoverable. To build trust I’m using H2testw:
H2testw is a small (less than 500kb!) free and handy portable app which you point at a target and it will write to every part of it, then read it back to verify the integrity. Check it out at The Portable Freeware Collection.