Las Vegas had fixed maximum show payoffs ($6 or $8) in the early 80's that were being manipulated by someone making large show wagers on longshots at Pimlico and his cohorts making larger show wagers in Vegas.
As I recall the great sprinter Dave's Friend barely held third in one of those races and in another race one of the longshots did show, killing the profit margin. I found a link to an archived Baltimore Sun article and I'm pretty sure Beyer had an article about it.
http://pqasb.pqarchiver.com/baltsun/...t+of+Nev.+scam