1. Be a somewhat established member.
2. Collect TEN posts written in the last couple of months by other people that have not received nearly enough merit for how good they are, and post quotes for them all in a new Meta thread.
The is the
official requirements as posted by theymos to become a MS
So I think a generosity-ranking for no merit soures has a good added value.
That also could be something relevant to mention when requesting to be considered to be a Merit Source.
Though the generosity score for aspiring merit sources isn't included in the requirements, but I'm sure Theymos also looks closely at that when selecting. Users can't aspire to be MS's with a 'very low' merit generosity score (that in one way or another means you hoard merits) and since users must be 'established members' and have earned quite a lot of merits (of course to achieve that status) the excuse of having no smerits doesn't then apply.
Generosity for a non Merit source is relevant...
I second that, also in their receiving/earning merits, some users have said they do not like giving out merits to users who
hoard their smerits.