if 20 bucks isnt much then burn it.,
if you still want to use it., use some 3rd part tool, to wipre data.,
what it does is, writes 0 and 1 to the usb, all over again and again., many times.,
so its impossible for some one to recover old data from usb.
I already burnt it, cut it, hammered it and flushed it down the toilet.
You can't believe how resilient this things are.
I was more intersted in whether there is real danger in reusing those cards or how to properly wipe them (answer: you are never really sure with flash drives and SD cards).