Growing a letting agency usually means increasing the number of properties under management and, for most letting agents, it is not good news when a landlord decides to sell.
If you are considering looking to sell the tenanted property to an investor you may wish to consider companies such as Portolio (https://portolio.co.uk/). Portolio work in partnership with letting agents, helping their landlords to sell the property with the tenant in situ, instead of ending the tenancy. This approach does not suit every landlord and/or property but it may well be worth considering.
By selling with the tenant in situ, landlords receive rental income right up to completion of sale, they will also often have less expenses and less hassle. The letting agency continues to receive a management fee, and may even have the opportunity to manage the property for the new owner. Everybody can be a winner.