I purchased a 1979 Mixes promo online back in the day for $9. Turns out it was the rare FR Delabel promo! I was pretty excited about that one.
On the flipside, back in 1997 I paid someone $200 for a sealed Pisces 12\" + 7\" and Rocket 7\" in the box. He emailed me back and said that he had it all packaged up and ready to go and someone stole it off his desk. Good part, he did give me a full refund. But that was a real let down that day.