Decades ago, when Marx Playsets, Hartland figures were hot and commanding high prices. Toy Shows would hold open trading/selling among Dealers the night before. Before long the average collector heard of this practice, and it killed the shows. Collectors quit coming since most heard/knew of this practice and the best pieces were gone, or prices raised even further by Dealers that had bought or traded for their inventories.
I was a dealer then, collectors let me know.