I'd take this superpower and publicize it, and offer to take bids from some controversial legends - Farah, El G, Shelby, Paula, Geb, Bekele, etc. - to let me use my power to prove that they (the highest bidder) were clean. Or if that didn't go anywhere, I'd start targeting certain people. Like I might say, hey Mo Farah and El G, I'm kind of torn over which of you I want to use it on - what do you suggest? The reactions would be priceless. Someone in a position like Farah should in theory jump at the chance to prove his cleanliness if he were indeed clean. Or someone like Shelby would consider it a sound investment to pay, say, $100K and be instantly redeemed (if she is actually clean). You could really exploit the superpower by pointing it at various famous people and seeing how they reacted before finally using it.