Its not rocket science to ban advertise bots who sells some stuff for real money (Which is against blizz policy)
Right Click > Report > Ban ? Guess you let them or you are behind this in first place.
The vast majority of these advertisements get spammed from accounts that have been stolen or compromised. Gold sellers, boosting websites etc. aren't really in the business of giving us money, they want to make money for themselves. The easiest way for them to do this is simply by using accounts they have gained the credentials too (most commonly via
Phishing). They then use those stolen accounts to spam their advertisements.
We realise seeing these adverts being spammed can quite the annoyance, and we're continually evolving our ways of combatting this. Most actually get caught without the need for any sort of report. That being said, right clicking and reporting any such messages you see, makes sure that the incident is on our radar. Your report may even help secure an account that has been stolen.