Improving Auto-Following via Twitter API

There are two issues here:

I get emails everyday about people following me, that's great and it really helps me to follow only those that add value, i.e. not selling me something I don't want. However most of those "new follower" emails are from people trying to sell me something. Can I one day block auto-following, perhaps with conditions for example, if the new follower has been blocked by others? That would help a lot in spam prevention.

Secondly, if I choose to auto-follow people and have been trying out a number of third party apps to do this, how can I then find out which is best? The only way is for Twitter to reveal which app initiated the new "follow". Recently I did find myself following new people, but I could not find out how as I forgot which service I set it up with. I did eventually find the service and am no longer auto-following due to the sheer number of network marketers.