Blizzard seems to have a certain problem on how to handle this boosting and gold selling problem. Mostly because people use Trial Accounts for advertising. The discussed having a certain amount of Achievement Points, Reporting tools etc.
I think the most effective way would be to connect the Battle.NET to some sort of unique ID. I think a mobile phone number would be a good thing. Once you connect that number when you create a new account, that number is „burned“. This would not make a huge difference for most people… you could have up to 4 WoW Accounts, and never get into trouble.
But for people that create massive amounts of Trial Accounts, or behave toxic on a regular basis. This could soon turn out to be a problem. True, you could buy a new SIM-Card everytime, but it would make those thinks pretty expensive.
From the game side, they should monitor the chat and reports more closely and I‘m betting that the whole sell-Run, gold-selling and toxicity would dim down to at least BC-Levels and they could tune down monitoring again.
If for some reason phones don‘t work, drivers licence, ID, credit-card number would work as well… depending on what country your living in.