うる ことぼ に かう ことば
uru kotoba ni kau kotoba
The great thing about being a foreigner living in Japan is that every interaction is an opportunity to learn something new, even when you're having an argument. Argument is a relative term of course; in America an argument with my ex-girlfriend meant raised voices, and maybe a slammed door or two, followed by extend periods of passive-aggressive behavior. In Japan, I've learned to think of arguments as long, low-key, strained conversations followed by extended periods of passive-aggressive behavior. Who's to say which country does it right?
This expression, which I learned after a long, LONG conversation with my landlord about what to do about all of the furniture that someone has to clear out of my house (he wants me to pay to have it removed and disposed of; I think I shouldn't be responsible for anything that was already there when I moved in), and I'm glad I learned it in that context, because otherwise, I never would've been able to extrapolate the meaning.
I mean, think about it: 売る言葉に買う言葉 (also sometimes expressed as 売り言葉に買い言葉). What does it mean? "Selling words to buying words."
In the context of a conversation, if one person is talking sales and the other is talking purchases, it sounds to me like you've got a transaction on your hands. Everybody's happy, right?
1. Trading barbs.
2. A bitter back and forth
3. A heated exchange of well-chosen words
Think of the argument as a matter of trade, with both participants engaging in a fair exchange. If one person makes a snide comment, the other person comes back with something equally snide, equally appropriate, and the argument escalates. This would be a good phrase to use when describing a marital squabble or a quarrel between two people who are very well known to each other. The way that 売る言葉 are perfectly tailored to respond to 買う言葉, fits in perfectly with the idea of two people who know exactly how to push each other's buttons.
Online definitions say that an 売り言葉に買い言葉 situation is often described as 喧嘩のタネ: the seeds of a quarrel or a fight.
Seems like there was a heated exchange of words that escalated into a brawl.