I've bought from amazon usually sandisk extremes. No trouble so far. Didn't seem fake when i got them. No strange fonts i could discern. Read & write speeds benchmarks are as expected. Capacity is as advertised. I don't depend on sales at all, i buy when i need or when the price isn't ridiculously high.
but this is a mixed views topic. I've known people here on this board to have diametrically opposite experiences. Leave alone reviews on online sites.
Cards failing unexpectedly, genuine as well. I don't swap cards around. My phones read cards out of the package, no format is needed. The card sit in there for years until i replace them three or so years later.