I had a similar experience recently on Facebook.
What really bothered me was the seemingly 'honest' group admin.
I was selling some big box Amiga stuff individually.
He asked what was the lowest I would take for the lot, and I asked him to make me a 'Sensible' offer.
He offered an amount that i would say was offensive, so I quoted a more realistic price. About 20% off, which I thought was generous enough.
He came back to me quite offensively to ask 'how the hell he could make a profit selling them on', and he reported my ad to Faceboo