It's not about assuming, it's about reading between the lines. You are the one that gave us the guy's hard luck story and then you proceeded to tell us that you bought a nice tool chest from him full of Snap-on, Matco, Mac, and Craftsman for $120. If you truly paid a fair price for the tools you would have walked away from your dealings with him feeling like you got some nice tools for a fair price and you would feel blessed that you were able to help out a friend, that's it. Many true friends would even overpay a little bit for the tools just to help the friend out as much as possible without making him feel like a charity case. A stuation like that between true friends involves humility, give and take, and compassion, not excitement, one-sided benefit, and deal bragging. When you say things like "if you want to see the crazy amount of stuff I got for cheap let me know" and "man he made me a deal" that implies that you do in fact realize that you underpaid. It also indicates that you aren't really trying to help him out after all, it has really just been about getting some for yourself.
Question- If any random person on earth walked up to you in your garage today and offered you $120 for that tool chest and all the tools in it, would you feel they were offering you a fair price and would you contemplate selling it to him? I bet not. The price you would be willing to sell the tools for to a random stranger is what the tools are really worth to you. If you paid anything less than that number in your head it is only you benefitting from the transaction, not your friend. I would be willing to bet that even a pawn shop would offer more than $120 for a chest that size full of good tools, and pawn shops as a whole aren't known for their friendliness and compassion. That's where some of us are coming from.