I've always viewed trading, especially of base commons, as the value being in the eye of the beholder.
I have cards you want that I am not attached to and you have cards I want. Let's swap, even if the last dollars and cents don't add up.
Amusingly, I have had trades where I thought, "man I'm getting a great deal here" and when I stumbled across the prices that some of the cards I traded away sell for I probably "lost" and vice versa, where I thought I gave up a bit much, but turns out I didn't, at least in $$ terms. Ultimately, in all trades I add PC cards I want and trade away cards I am not attached to, so that makes a win for me.
The only time I worry too much about prices is if I know a card is worth a bit more, or if the trade partner seems particularly concerned, I have never initiated a trade with them.