The most common way of compensating assistants from what I've seen is to give them an annual salary and then with each deal that closes give a bonus depending on the effectiveness, efficiency, and performance on the transaction. I personally believe that the amount of the bonus should depend on the size of the transaction, how difficult it was, etc., but most give assistants a fixed bonus of anywhere from $50-300 for each deal. I know of some other people who go completely on commission, they split their take on the commission with their assistants 60/40 or 70/30, though I only see that rarely.
There are also many Realtors that I know of that have taken on new trainees or interns that are wanting to enter the real estate industry but need experience. For them, there is no salary but there may be bonuses with every closed deal. Hope this helps Cindi!