If I understand you question, FS is dick penetrating pussy sex. L1= HJ, L2=BJ and L3=FS. So non-FS means that either it is L1 only or L1 and L2, but no L3. And that is what the ad says, meaning she does not spread her legs for every john that inquires or sets an appointment. But if you play your cards right and have a little game, then L3 is available.
However, I would not review or provide intel that she did FS with you, especially to this crowd. Keep it between you and her. If you do not, then you probably will not be getting that upgraded service anymore. If you have to review her, say you did only the activities in her ad.
Definitely take what providers post at face value. If something more happens consensually because two people are in the moment, then consider it a bonus.
But don't book with someone who says "No ___" and then get mad when it doesn't happen. You were warned ahead of time.
No fs = chick reserves the right to meet you in person first and decide if she wants your limp dick inside her and if you past muster will then proceed to throw out some ridiculous rate to entice you into wanting to tag that ass...