"That's just semantics" is a common way of saying "you're arguing over semantics instead of the point." When arguing semantics is disguised as a genuine rebuttal, it's a fallacy.
If I say the sky is blue, and you assert the sky has no color, you're not actually contradicting my assertion you're disagreeing about the meaning of the word 'sky'. That's arguing semantics instead of addressing the point.
Yes, by "that's just semantics", I meant that it doesn't matter which party you call the customer. The thrust of the argument is still that Groupon is screwing over merchants and that I'm not convinced that merchants will continue to work with Groupon.
If I say the sky is blue, and you assert the sky has no color, you're not actually contradicting my assertion you're disagreeing about the meaning of the word 'sky'. That's arguing semantics instead of addressing the point.