yeah, personally i won't sell them at 0.5fg per, i offered mine at 0.1 so doubled that price and op didn't want to buy it, but your friend didn't lose out a ton of fg imo.
your friend made a big err if he thought op was paying 1fg per flawless square AND 1fg per star gems, they are not equivalent and should have done the calculation. dude wanted to pay the equivalent of a flawless star with 50 stat worth of flawless squares, which is 81 for 1fg..... which is 0.012fg per flawless square. but you can still see he got a much closer to fair deal getting 0.05 per instead of 0.012.
imo it's not a huge loss, he maybe out 20fg, or what do you think he's out?