Many companies hold on to their "problem child" salespeople for far, far too long. And I have heard many a "problem child" salesperson directly threaten or imply, "If I am not appreciated here, I will go work for our top competitor."
I often find myself wanting to say, "I will drive you there myself."
The real question is... Is your "problem child" salesperson a true "sales wolf"?
When should you let your "problem child" salesperson go work for you competitor depends on whether or not the "problem child" is a true "sales wolf". A true "sales wolf" has the capacity to sell in the top 20th percentile on a consistent basis. A true "sales wolf" adds extreme value to the Customer through their counsel.
Let's define "problem child". In my travels, I have met many a "problem child" salespeople. 
A "problem child" salesperson is essentially a prima donna who really does not deserve to act like one.
- They believe the company would fail without them.
- They believe their value is far higher than it actually is.
- They often lean closer to the Customer than to the company.
- They believe that past deeds performed five, ten, or twenty years ago merit permanent employment status.
- And they often mistreat others in the company to "serve the Customer".
The problem child salesperson comes in three categories. The first of the three categories need to be immediately encouraged to work for the competition.
The "never did and never will get it salesperson"
The worst of the three categories is the salesperson who has never been a "sales wolf" and never will be one.
You either are or you are not a "sales wolf". It is about potential and skill - not skill alone.
The only reason this type of "salesperson" does so well is because they have worked the Client relationship for so long and their primary contact is/was very "old school". They are often adept at giving away value wherever possible. They actually seem to fight on the same side as the Customer yet they are there to ensure they get 100 percent of the full compensation. They do not need to do cold calling and prospecting because they have so many important things to do for "their" Customers.
The brand alone will always sell more than the "never did and never will get it salespeople". Brands like Coca Cola, Apple, and BMW... Have legions of fans. Their brands do almost all of the "selling".
When the primary contact of the "never did and never will get it salespeople's" Customer retires or moves on, the new contact will steer clear of them as much as possible. The Customer wants more than just a relationship. They want value added, extreme value added.
For the record, some of the "never did and never will get it salespeople" are the nicest people you will ever meet. They do not knowingly mistreat or harm anyone in a direct manner. However, they put the company and Customer at risk by what they do not do. They rarely add value to the Customer relationship other than through price concessions and company swag. These people unwittingly put the company and their coworkers at risk by commoditizing their products/services and reducing if not destroying profitability.
Send these people packing to your competitors. Immediately.
The true "sales wolf" with an attitude problem or lost mojo
Some true "sales wolves" are "wired" to be problem-seeking "machines", particularly the "hunters". Sometimes the problem-seeking becomes more introspective than it should and the result is self doubt, which can take over and damage the true potential of an otherwise top sales performer. I often find that the more "hard-charging" the personality style, the more likely the true "sales wolf" will have relationship challenges with others who are not "wired" like them.
The challenge is identifying if this is a permanent issue or more temporary. If it seems temporary, then of course keep the "sales wolf" on your sales team. Help them through employee assistance. Help them get a "base hit" to regain their confidence. Identify coaching and training opportunities to help them succeed.
As a sales manager who cares (and you must), sometimes you can help. Sometimes you cannot. Sometimes the attitude problem is long-term and will only get in the way.
If the attitude problem or lost mojo seems truly permanent, especially if the salesperson is lashing out at the company, they need to go work for your competitor. There is nothing better than the bad attitude or lost mojo "sales wolf" going to work angry for a competitor.
Sometimes you can help a "sales wolf" get their mojo back by helping them improve how they talk to themselves. A powerful book is The Four Agreements by Don Miguel Ruiz or the latest version written by Ruiz and his son Don Jose Ruiz - The Fifth Agreement.
It is one thing to be hard on oneself. It is another to use your words against yourself. My personal belief is if you would not say a particular phrase to a four year old, then do not do so with yourself.
The true "sales wolf"
You will naturally want to hang on to and cherish your true "sales wolf".
A true "sales wolf" is supremely "wired" to sell - whether it is account management, inside sales, or sales "hunter". You never, ever want to lose a true "sales wolf". If they are high maintenance and consistently producing, engage them, love them, honor them, and figure out how to make them as happy as possible. If your true sales wolf is a "prima donna", you may need to consider curbing the undesired behaviors. But I would proceed with extreme caution.
Yes, I have seen instances where a true sales wolf was such a prima donna that they should have worked for the competition, but the fact is, it is rare.
The natural question you likely have is, "Should I treat my "sales wolves" better than the other salespeople?" The answer is "YES!" Let's say you have a Ferrari 458, a new Corvette, and a Porsche 911. Which car do you protect the most? Of course the Ferrari 458 because it is worth more than the others combined.
And just an FYI - only hire true "sales wolves". In other words - only "drive" the best-of-the-best.
The ONLY way to know if you are dealing with a true "sales wolf"
There is only one way to know objectively whether or not you have a true "sales wolf" on your hands. Whether they are an account manager, inside sales, or sales "hunter", the only way to truly know if an existing salesperson is a true "sales wolf" is to use a sales personality and aptitude test with validity backed by brain research. Otherwise, you are just guessing. And guessing is for losers. 
