I've started to network with some local chefs here in San Diego and have multiple offers to work a stage once or twice a week. I have one semester of baking under my belt and almost one semester of savory (regular cooking) done. I have basic knife skills. What do professional chefs look at when people are working a stage?
Working a stage
They will be judging your current proficiency levels, attitude, and potential. A stage is all about performance. It's your time to showcase your strengths, not let your weaknesses cause any real blunders that you can not overcome, and to realize where (if at all) you might fit into the kitchen.
As long as you do your best there is never anything to be embarrassed about.
As to wasting someone's time, anyone that would feel that way probably doesn't have the qualities that I look for in a boss.
Make sure to ask lots of questions and learn as much as you can. Show your interest and passion during your stage. You will not be expected to be a "machine" and you will probably be treated as someone who doesn't know anything at all. Chefs want stagières that are obedient, punctual, passionate, hard working and willing to learn. If you are like this you will probably be offered a job after your stage and if not, at least you might have a recommendation.