Aside from the fact that I believe you mean Genius Bar rather than Genuine Bar...
Speaking as someone with an extensive IT history I can tell you this:
1. If the technician can't reproduce the problem, they have almost no way to fix it.
2. Make sure the problems you are going to are true problems and not something silly. I used to have a user at my last job who always put in a ticket saying her mouse wasn't working, when in reality she repeatedly tried to right click with the scroll wheel. I'm not saying that this is your case but it happens VERY often.
3. Mention your problem here, we may be able to help or find a good way for you to explain it to a genius.
4. Be SUPER nice to them. Nice = results. Mean = no results or not as good of results as you could have gotten by being nice. If anyone tells you otherwise they've NEVER worked in customer service.
An example would be that Apple credited me $190, rush shipped me a brand new monitor (when I was returning a faulty refurb that was outside the return period) all because I was very polite and patient and the lady on the other end commented on that, said she felt bad about my faulty monitor and tried to see if there was anything extra she could do.