I also know that many solo ad providers are as shady as a big oak tree. :p
The bad ones will do the following:
* Send blind copy to their list to drive up the click-throughs for the buyer;
* Send deceptive ads to their list to ensure a higher click-through or sign-up rate;
* Send bot traffic to offer pages;
* Pay mturk peeps to subscribe to their customer's lists.
As someone who buys solo ads, how do you determine which solo ad providers are the good ones and which ones are the bad ones?