so true, however buying from such outlets might leave you w/o warranty even if the piece is actually a genuine Canon - but "grey" one...
Grey imports may still be warranted in some territories.
so when price is too good to be true it makes sense to buy a genuine 3rd party flash in a more reliable outlet.
Sure, I'd be suspicious of any ridiculously cheap offers, but it may be a case of
not being too good to be true. Just a decent price for what is sold as a genuine product.
They'll also find their way into the secondhand market and again you won't be getting what you'd expect.
I doubt there's any chance they'll be as well built as a genuine product, or even as well made as a non-OEM product, so may prove to be unreliable or worse damage the camera they're attached to.