Being fairly new at this myself, I can understand your hesitation. My first evocation was with Duke Sallos and I had no idea whether he showed up or not. I was not able to tell and chances are that you will not be able to also. Just go ahead and do it and figure that he is there and that he heard you.
I didn’t know that Duke Sallos had heard my request until when it happened. Then he really made his presence known to me and you might end up having the same thing happen. I didn’t go into the ritual already thinking on how to get rid of him, I just did the ritual and went about my day.
I know it can be hard to erase your doubts, but try to do so. Have respect, state what you want, what you will give, and let it go. If he wants to help you, you will know soon enough. If he does, great, if not, then there are other spirits to call upon, but already having a negative mindset will not help your cause.