After reading all the comments, I can see that 99% of you, get offended when a seller or buyer is rude to you.
Yes, it happens to me too, but instead of getting offended, I mess with them a bit and sometimes we even end up friends. A lot of the time, they end up liking me and selling the item to me for cheap anyway, so It's actually worth it not to get angry.

Here's an example of what normally happens to me...

Mistermerch: Selling cottage bed. 350k or near offer
Me: You do know that they sell for a LOT loss in auc, don't you? I'll give you 250k
Mistermerch: Low ball noob. U don't know anything selling. 350k is a good price
Me: Are you saying I have balls? I'm a girl, not a guy. Don't be rude...
Me: I'm sorry to be the one to tell you this, but sadly you will not sell it for 350k
Mistermerch: Foking girls don't know one thing about anything
Me: Well, we know a lot about makeup and boys and I know that you won't sell your bed
Mistermerch: Idc what u say, I'm gonna sell it for 350k
Me: Good luck on selling it then
Mistermerch sent you a friend request
You accepted Mistermerch's friend request

Three days later...
Mistermerch: I'm sorry for what I said before, u were right
Me: So you didn't end up selling it? I'll still buy it for 250k
Mistermerch: No I didn't. Fine. U can have it for 250...
Mistermerch wants to trade with you
You accepted Mistermerch's trade
Me: It was fun doing business with you. xD
Mistermerch: Shush ;3

Sometimes it's good to have a bit of fun.
-Aba