Yeah but there is difference in wash trading and Net Trades that duplicate the volume. Net Trades are not illegal and are part of the OTC market due to the process of Riskless Principal, sell first and then buy. You will get duplicate volume reporting when the sell and buy are not the same price.
But as you say it is an indicator and most of us watch for the dumping and wait for the offender to move off L2. You can sometimes time a break in dumping and make a few on a quick bounce before they return with more shares.
If you read some of the recent litigation on these tickers, there were groups timing their entry and exits with the dumping entity as they colluded as to when the dumping would stop and when it would start again. As you often say play with the big guys and their timing, the dark forces are often well "informed" groups who have a heads up.
News 
Market Data 
Discover 
