I'm sorry, but it seems to me that the seller was a jerk.
If you're a seller, and someone doesn't pay, you send out a friendly reminder before getting nasty (and nasty includes trying to guilt out the buyer).
And if you get a polite apology with payment, the correct response is "I understand, I sometimes forget things also - thanks for remembering and for your kind note".
Everyone blows it on occasion (and we tend to dwell on those failures far more than our successes - odd, isn't it?). In any relationship (business or otherwise) you have to assume that the other person is sometimes going to make mistakes. The measure of their character isn't in the mistakes, but in the way they handle them. If they apologize and try to make it right, and accept your apologies when it's your turn to screw up, they're the kind of people you want to keep around - and the kind of people whose opinion you might want to pay attention to.
But someone who sends an unpleasant note in response to an apology, or loads on the guilt - that's not someone whose opinon of you is worth caring about (though of course it's hard to avoid caring anyway - another odd thing, isn't it?).
Don't beat yourself up because you're dealing with someone who lacks decency.
who else is up for the early walks???
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