Imams and scholars in Islam

[glo]

There are no Muslims nuns or Muslim priests or Muslim Bishops or Muslim popes. In fact there are no ordained Muslim clergy. We all strive to serve Allaah(swt) to the best of our ability.

Woodrow wrote this in another thread, and it got me wondering.

I understand the idea of not having ordained clergy in Islam, but can I ask how a future imam or scholar shows himself to be worthy of the title or position?
Who decides whether a scholar is learned enough to call himself a scholar?
Or whether somebody is worthy to become the imam in a masjid?
Or whether the teachings are correct and trustworthy?

Are there training schools who ensure that the correct teaching is passed on?
Are there specific qualifications which can be gained?

Sorry about so many questions ... I hope they make clear what I am trying to find out.

Thank you, as always.