Biff Yeager, the charming and friendly actor who played Chief Engineer Lieutenant Commander Argyle in only two episodes of TNG, was once tasked with the job of signing a large number of Star Trek trading cards featuring his likeness. He carried out this task effectively, and his cards went out across the globe for eager Argyle fans to find.
Years later, Adam bought both himself and Ben cases of similar Star Trek trading cards, amongst which other signed cards were scattered, and following their reviews of "Where No One Has Gone Before" and "Datalore", the two Argyle-featured episodes, they turned their fancies to finding a Biff Yeager-signed card, AKA a "Natural Yeager."
As more packs were opened over several episodes, it was brought to everyone's attention by a viewer that, in fact, Biff Yeager's signed cards were not included in the sets that Adam and Ben owned, and thus their search for a Natural Yeager would be futile at best.
However, Adam took it upon himself to wildly scour eBay for Biff Yeager signed cards, buying at his own estimate 30 cards in a maddening attempt to artificially inflate the Biff Yeager market. He soon after re-listed one of his cards at a price of $999.00 (but with free shipping). As of this writing, it is still unsold, and is most certainly an Unnatural Yeager.
A viewer listed one of the Yeagers that slipped through Adam's trawl for $998 and, apparently, sold it for that price. The Biff Yeager eBay market remains lucrative, at the very least in the most speculative sense.