Depends on what your definition of "make a living" is.
Everyone has a different standard of living, and for some
I am sure its very easy to make enough promoting Safelists/ mailers
and make enough to live comfortably.
I wouldn't base my entire business on promoting other peoples
sites though, unless it was on the back end of my personal list
or a site of my own first.
If you focus on building downlines in a site and making good commissions
what happens if they close, or change their commission structure or.. any other
number of possibilities.
If you are building your own list first you can communicate with your list
and let them know what happened and what you are doing about it, and have them
join a different site with you, which you wouldn't be able to do, if the site
just closed.