The women are not that unsuspecting, they go there specifically for abortions. We know it, and they know it.
Some women go there because they've seen the ads where PP claims to be there to help. Or because some PP hard-core saleswoman came to their school and told them how great PP is, etc.
PP is all about selling abortion, and they have a very sophisticated methodology for it. But women or girls going to PP offices are often young and naive, and have no idea that PP only looks at them as cash cows.
I do know from personal experience that if a young girl or woman goes to PP because she suspects she might be pregnant, and she has fallen for their lines, she will have to go to a "counselor" who, basically, will try to talk her into abortion before ever giving her a pregnancy test. It is a very high-pressure sales session--the girl talks about why she thinks she might be pregnant--the counselor says, "So, you will be wanting to have an abortion, then?" The girl says no, she just wants the test so that she will know, and, again, "So, you are considering abortion?" Etc. If the girl keeps denying that abortion is an option, the counselor will probably send her away without giving the test.
It is true that many girls go to PP specifically for abortion, and become repeat customers. But that isn't always the case--some go to PP because they really want help, they are confused and don't know where to turn. And all PP does is pressure them into abortion without telling them their options.