Think its better to sponsor yourself as you can be sure they are genuine. Even the most famous of the sellers of PSAs on SFI buy the advertising from outside agencies and really not worth the money you pay for them as there is no guarantee of even getting one real affiliate from those. In my experiences in 3 months every single one i got was non responsive and also 50% with bogus email ids that dont work. You can try the S-Builder Co-op if you still want gain PSAs every month.
