In a group in LinkedIn I answered a question from a spa owner that asked how to deal with a possessive therapist that did not want to share her customer when she went away on vacation. Here is my response:
I have not read all the comments here but most of the comments seem to revolve around the issue with the therapist but the real issue is you. As one very person @Bennet said you are not acting as an owner. First of all, never give the power to the therapist. Many times therapist start at a spa just to get a client base and then leave and take the clients with them anyway so you always have to be ready for such things and factor them into your business model. So as an owner you or your manager (if you are not on the premises often) have to establish the rapport with the client. The client is yours not the therapists. By establishing a rapport they tend to see you in charge and feel more special that management knows them, making a change of therapist is then easier. Also you can work on them to steer them around to various therapists "for a change of pace", like @Frost said "massage" into the head of the customer that various therapists have various strength so when they arrive and you ask what parts need more work, then you or your manager become their best advisor by assigning the best therapist for that particular issue. You or your manager are in control of the clients not the therapists. You guide your business not your clients or your therapists. Of course all of this has to be done very carefully because for example, I am sooooh particular about the massage I get that if I have a bad experience with a therapist I will never want to use her again, but I would listen to the advice of the manager who knows her therapists as to which fit my requirements better and try her. This is where you or your manager become the bosses for real. Everything in your business starts and ends with you, customers need management as much as staff. So start with managing customer by servicing them in a way that they believe you have their best interest in mind and switch therapist for them benefits. Also interacting with her clients will let you put a bit of separation between her and them so that they are more likely to be loyal to the spa that treats him or her with personal attention, even from management, than the therapist. Unfortunately there is a certain sector of clients that just imprint on a therapist and there is nothing you can do about that, but for most this is not the case. So after managing the clients you manage the therapists as well, make them a team player and do things that makes them be collaborative and make them feel pride in the spa rather than just their skills. If they get used to you assigning customers and being in control of who sees who then they know who is boss and accept it better when they have to go and will even make suggestions of what therapist the customer sees if they are not around. Make sure that they are trained that if they will be gone they give you a suggestion, if you agree then the therapist before leaving will take the extra step of taking the client and introducing the next person who will treat him or her while she or he are gone and therefore the client feels as if he or she were handed over by their favorite therapist and will be in good hands. Lastly I would say for this case all of this is too late, so as a manager I would still go to the customer and tell them that she will be gone but you will still want to see him or her next time and give them the opportunity to try someone new, and since they are doing that if they are too hesitant and say they are not coming until she returns offer a special bonus for trying someone new (does not have to be a discount could be an extra treatment) that will make them try and that way you take control of them!
Bottom line--manage your clients first so they are loyal to the spa not the therapists, manage the therapist so they are loyal to the spa and not get a sense that they control clients or the running of the spa.