1. If the person 'looked at their avi' and told you what they saw instead of what was in rl...seems to me you have your answer, in which case, why ask the forum.
2. You said you were going to pleasure 'her" so at that point it sounds like you were interested in the she part of the shemale so your question is irrelevant.
3. This is a virtual world...what difference does it make what gender someone is unless it henders the role play...in which case, if you don't like the skill of the player, move on.
I could be wrong, but i believe you can determine the gender the person signed up in SL with initially by the little symbol shown on a mini-map and perhaps elsewhere. That doesn't mean the person designated their real gender to begin with but usually I would think most people do. The bottom line is, you can't tell what actual gender anyone is in a virtual world. If you want actual 'truth in advertising' then go rl.
5. If you weren't attempting to shock, then all the question needed to be is, "how do i tell the rl gender of an avatar." There was no reason to go into detail...