Dear PTOBoarder:
A tricky tray is what we here in Indiana call a "Chinese Auction", and I think it's known by other names in other areas. Basically, it works like a raffle. You buy tickets and place them in a bucket for an item that you'd like to win. At the end of the event, one ticket is drawn for each item. I'd never heard that term before either. As for why it's called a tricky tray or a Chinese auction, I'm clueless.