I disagree. There's no reason why anyone should have an expectation that guild members will take a loss on goods, 'just because.' While I'm always willing to throw a guildmate or friend a deal, if I'm selling goods for FPs, I'm not giving away my stuff to anyone, guildmate or not. Just like everyone else, the OP should be buying their Arc goods for FPs. They should not be trying to 'guilt' their guildmates into taking their bad trades.
Please don't perpetuate the attitude that just because a player is more advanced, they somehow owe others something for free, whether that player is inside the guild or not. I've gotten a ton of help from others by never asking for it, or expecting it. That attitude is not only presumptuous, but kind of offensive.
I got my CF and Traz goods from a guildmate. I did my research and found the going rate on my world was 200 FPs for a set. I emailed a couple guildmates in PE asking if anyone wanted to sell me PE goods. One guild member responded. I told him what I needed and what the going rate was, saying I'd rather buy them in guild to keep the FPs in guild, instead of paying for goods to someone outside. They came back saying they would sell them for 100 FPs.
I was thankful to be offered a deal and happy to accept. I got 2 full sets for the price of one. But I still paid. Deal or no deal, I was willing to pay a guildmate the going rate for the goods I needed just to keep the 'love' inside the guild. No reason why the OP shouldn't be willing to do the same. The OP is not asking for help, they're looking for a handout.
It's not a bad guild just because no one wants to give handouts to a needy player who can't pull their weight.