Now I've seen it all...someone offended for offering to help them?

[Nanga]

buying those for higher prices just shows ones stupidity. there's no higher gain attached to the allagan coins. I just buy all the vendor-priced ones to punish the seller (he loses 3-5% of the value, I just sell them at the same price to the vendor)

Don't take it as an exploit. Know that this is how gil traders move large amounts of money around.