If someone wants to make an offer on something I list as going in my PC or not FS/FT, I don't have a problem taking an offer. I'll never say 'I would never ever sell this for any price' because I know that is a lie. If a card is worth $100 and someone offers me $5000.. it's being sold.
So, if I list something as PC, that just means 'I have no interest in selling this at current market values so, if you want this in your collection you'll need to really overpay me'
And people demanding you undersell so they can buy and make a profit isn't limited to the card market.