I see many ads especially on CL where the girl will say she is fully functional and 100% bottom.  Does this mean that mutual oral is on the menu but she isn't into topping guys?  If she is fully functional, why wouldn't she want to use it?

The term "fully functional" means different things to different people.  That is rather the norm in this scene, don't you think?  The solution? Easy: either when you make your appointment or (if she doesn't want to discuss such things over the phone, which is smart) when you get there, and before you "take care of business," find out what she means by "fully functional," and if you can't live with her definition, leave a tip and leave.

because he/she believes he/she is a girl, and girls get fucked by boys they dont fuck boys!
f.i.o.

It means one thing but the problem is a lot of providers will say it knowing they cant follow through and unfortunately if she's one of those she aint gonna tell you nothing is happening. She gonna take your dough and pretend to make an attempt and then say "oh you shoulda been here earlier" or "I took my hormones today".

Well you could have told me that early... errr...

Its why I say if you desire that only use vrifiable girls and even then its not a gurantee.