I bought a set of Elixir's several years ago on Ebay. (Yes, yes, I know!).
The first string kept on stretching until it snapped during installation. I wrote to Elixir and included the broken string. They sent me a new set of strings + a key ring + two 'Elixir' stickers for my case. I wrote back asking them if they tested the string to see if it was a fake however, they never replied. FWIW, I haven't bought Elixirs on ebay since.