David Wells used to live near me and golfed at the golf course in my neighborhood. He was the first baseball player that I met there. This was around 1992. I didn't have it at the time, but I remembered that in 1990, Score released a baseball card of him where the image on the back of the card was reversed. I thought it would be cool to see if I could get that card signed, as well as the corrected version.
I went to a nearby card shop and found the card in a display case without a price on it. The dealer looked it up in that month's current Beckett Price Guide, but couldn't find a listing for it, so he sold it to me for a quarter. Unfortunately for him, he was looking in the wrong section. The card had a book value of $1.75.
I probably had the card less than a week before seeing David at the golf course and having him sign it and its corrected counterpart.
Looking back, I wish I would have had him sign the backs of the cards instead. Still, it's a cool thing to have. Pretty sure it's the only error card I've ever gotten signed.