[Discussion] I just got scammed in a way that left me baffled

Edit: he gave me the Five-Seven for free

I saw a store post here on Reddit for Five-Seven ch (Reddit account has been deleted in the mean time, but the post is also on steam (image 1)). This person offered a lower price if you'd buy them all. I asked about it and he added me. I didn't want the Stattrak ones so we were discussing the price for the 4 non-Stattrak ones. He wanted 13 and send an offer for all 5 of his Five-Seven ch in exchange for my 13 keys. Naturally, I declined since he send me too many and I made him aware of it(imgur 2). He seemed extremely grateful that I didn't take the offer, so in return he decided to be generous too and send the 4 Five-Sevens that we agreed on in exchange for only 12 keys. He even told me to double check it. I, however, felt like this wasn't necessary since I just caught him a break and he seemed very happy/relieved. Little did I know that he took this opportunity to swap his most valuable Five-Seven out and send the new offer. I accepted it (imgur 3) and when I went to check the skins, I noticed the Five-Seven that I wanted most wasn't in it (imgur 4 shows where it is). I told him about it thinking it was an honest mistake... after all he did send me too many just a few minutes before... In response he blocked me (imgur 5), closed the post and deleted his Reddit account. I'm somewhat salty about the monetary loss, but I'm completely baffled that someone would stoop THIS low. In the end, as they say: "No good deed goes unpunished".

Bonus: since we discussed on mobile and he deleted and blocked me the chat is gone forever and I can't even get him steamrep banned.

TL:DR Had the opportunity to get away with more skins than I bargained for, didn't and got scammed in return.

Imgur

Edit: He had a change of heart said he is very sorry and gave me the right Five-Seven for free. I offered him his #863 back.