Landlords aren't as loyal to a particular letting agent as you think.
My intuition tells me they are a hell of a lot more loyal to their own basic needs of getting the rent in and having no hassle. .... So if you want to persuade a landlord to swap letting agents .. that's exactly the last thing (ie swap agents) you want to try and persuade them to do... sounds weird I know
.. but every letting agent I have ever met has always told me about landlords they have got on their books because they did exactly that .. instead of trying to persuade them (or market to them) their services.. they met the landlord (say on a free val for sales, viewing on a property, socially, networking etc)
.. found out they were a landlord, built a relationship (like a good human being) , fostered and grew that relationship to a point some time down the line (months/years later).. that landlord brought their property to them to be managed.
It looks like this equation works ..
1. Meet a landlord and talk to them
2. Build a relationship
3. Continue to build and nurture that relationship, slowly building trust
4. Be patient and continue to repeat Step 3 for months (if not years)
5. Get the property to manage the next time the tenant hands in their notice as long as you have done Steps 3 and 4
All you need to do is work out how to make a landlord want to come and talk to you?