How can this question still be asked? And before you all get wobbly over my comment, this is about a bigger problem . People not doing any research of their own, and being scammed. It is what the Google search engine does best. Take advantage of the wonderful technology you have at your disposal. Read reviews and look at the YouTube videos and ask questions . Knowledge is power.
I don't think I have ever seen anyone say agents are worthless. They have a place. The point normally made is for people to do it themselves ,it's not that difficult. But to get back to your point I'm not sure how an agent could have prevented this.
If a Visa gets cancelled it's obviously for a good reason. If your visa is done honestly and you meet the criteria Why would there be a problem? Something to consider.....