Correct, if you are using these so called agents to facilitate your visa extension because you don't have the necessary financial or other requirements to comply and they by what ever means is used to obtain your extension, it's illegal.
Now if the I. O. grants the extension based of false information, either from the goodness of his heart (very unlikely) but by accepting money to sign-off on the paperwork - - that's a bribe.
The cure of course is that the passport holder must present themselves along with the correct information as is already done by the vast majority of people applying for an extension.
All dodgy a/holes should be shown the exit door.