Wow you really have issues.
To the rest of you, for what its worth, sorry he is wasting all your time, but how many of you have a regular store you go to?
Imagine you go to your local gaming store, you are very comfortable there, you have been there for a few years and really like the place. You have lots of friends and people you trust and consider it a great place to hang out. You see some new people who are looking for trades so you open up your folder to see if anything may work out.
Now you start a conversation about making a trade with a few guys and out of them only one has something that seems workable. He is obviously new but seems to be interested in some of your cards so you make an offer that is Fair. you look up the prices at TCG and use the avg for everything. The guy first asks (in a easily to be taken as condescending way) whether your cards are MINT because HIS sure are. You know the card is fine so you try to continue the trade, ignoring the arrogant behavior. He starts adding cards from your folder that makes the trade a little uneven, and asks you to accept. You assume he is interested in a bigger trade but nothing to balance it out so you adjust it a bit, and offer another equal trade. He repeatedly adds cards from your folder and asks you to accept the trade, even though its obvious to you that the trade is horribly uneven in his favor and he wont let you add more cards from his side. He always changes it to something uneven and stupid.
Now at this point most of you would be wondering what the hell this joker is thinking making more and more unreasonable offers (he got worse not better) and he tells you in what can only be taken as an arrogant tone how HIS card was worth more two months ago and so you should give him a lot more in value, even though the value today is less. (its called market price dumbass) Now you had been polite and patient with him so far but at this point you realize he is either 1. an asshole/shark that is trying to screw you over due to his arrogance, or 2. he is an idiot that doesnt understand the basic common sense of trading and changes in market value.
What do you do?
You could just quit the trade as usual, you have done it a hundred times before and will do it countless more, but for some reason this guy's attitude really bothered you. Perhaps the arrogance and selfish behavior makes you realize this person is a bit of an asshole and you dont like that people like him might start screwing up your fav hang out place and probably turn other people off due to his behavior (most people will ignore it as you do, shit happens and its only a failed trade, but its always good to be warned of jerks ahead of time.)
Also, seeing as how you met the new group because someone was talking about being unable to make trades due to poor/no responses, and being someone who hangs out here a decent amount you know exactly what they are talking about, its quite possible that you also feel that while many people just quit and you wont see them again due to normal life issues, there are others who get turned off due to jerks like the guy you just met, and those people end up quitting the site due to one or two bad apples. (he isnt that important but every little bit hurts)
So as you choose to walk away you take the extra step (which you dont normally do) of kindly warning your fellow members that this guy is a little crazy (He really does need to chill out). You dont curse him out, but your choices are crazy or jackass, and being the calm individual you are, you figure being called crazy is the more polite thing to do. You dont give the guy a negative because that is a little extreme for a failed trade but still a zero is a fair warning for poor social behavior.
Thinking back, if the person didnt want to be called crazy he shouldnt have acted like a crazy person, and when he starts cursing you out, well all you can really do is laugh about the whole thing cause its pretty damn funny. You continue on with your other successfull trades and remember that its good to have a place where the majority of people are sensible and reasonable and not to take the bad apples too seriously.