I have had this experience as well and really don't like to SF anyone unless one of my friends know them. Other times I will make Chanty SF them first, and "screen" them (I know you love doing this Kip). After a few weeks/months if we are still playing with that person then I will SF them.
I have found that through speedchat and playing strategies, you develop a certain impression/opinion of the person running the toon. Getting to know them through SF does not always prove beneficial, and more times than not they end up being someone you really didn't want to know any better. I prefer to keep the anonymity and intrigue. That being said, I have others that I have SF'd after being friends for a long time and those are now my favorite people (BOBBY!!!!! if it weren't for you I wouldn't be here, and thanks to Leeann for constantly Xing me

)
Just as in life, everything is a gamble. My usually pessimistic self is turning optimistic, so I say SF them. If they turn out to be someone you don't like, well we all know what that cute little X button is for. If you're Leeann, you know it all to well. (you know I'll never let that go)