Why people are so salty?!

It is not the first time I've seen someone like this... Long story short:

I trade TF2 keys <--> EUR, someome added me on Steam (ofc without writing a comment at my profile or steamtrades) and asked me about pricing and so on,... he decided to NOT buy at that time. I said TF2 Keys were 1,80€ I got some sales during the day and decided to raise the price to 1,85€ due to my stock dropping at great speed. I update the pricing everywhere accordingly.

At the afternoon the guy send a message and sent the money without waiting for me to say it was OK or the price were changed. Anyway the price is always up-to-date on my discord state, Steam in-game status and my steamtrades.com thread ( https://www.steamtrades.com/trade/Y2rA8/ )

So well he basically ended angry and leaving a -rep for no reason... at my profile:
https://www.steamtrades.com/user/76561198983211883

Proofs: https://imgur.com/a/WWh2IkZ

Why there are people that kind out there? I do not see the point...