[kurter]

Exactl.
Best weapon against trolling is ignoring.

Nope. You have to be polite and answer at least one time in a reasonable fashion. After that you can ignore him.

I know it's really, really hard to fight the urge just to type "SHUT THE FUCK UP AND DIE" but you can't lose your cred as a seller.

The customer is king as bad as it can be...a lot of sellers forget that as well and treat you unfair just because you "lowballed".

Sigh.