Among many other traits articulately described already by others in response to your question, I like agents who have mastered the art of saying NO.
"NO - I'm not spending half my day driving you around looking at properties when you have not yet been qualified by a reputable lender to finance a pack of gum."
"NO - I'm not showing you properties until you sign an exclusive buyer's representative agreement."
"NO - I'm not going to submit your silly low-ball offer when the seller already has a dozen offers at or above the asking price."
Agents tend to go the extra mile for clients, even when the destination is off the end of a very high cliff. The ability to assess a client's needs and purchase qualifications is a vital agent survival skill, capped off by knowing when to keep saying yes and when to say finally deliver a firm NO in an appropriate and helpful manner.
You may find these NO-sayers within the local agent population, which is the best place to look if you don't have a lot of time to mentor a new licensee. There's nothing that says you can't talk to buyer's agents who purchased your listing after the transaction is done.