Like the poster above me said, there are RMT bots that que a party of blms over & over for wanderers palace and they farm the first half of it all the time. No normal player would have that many and sell them in stacks of 99. RMT are also doing that with materia cause they SB gear and sell the materia for Novus.

I saw stacks of 99 materia on sale cant remember what tier it was but yea, to answer your question its probably RMT bots.