We value properties using our experience of the current market, analysis of the 30-50 properties we let each month and the huge number of properties we currently manage. It is a fact that Tenants dictate the rental value - not Landlords and their financial needs and not the agent who guesses or tries to impress you with an inflated valuation only for the property to sit empty for 2 months and the rent decreased to a suitable level to let! Some agents use Rightmove to "prove" rent values. Remember - Rightmove only contains details of properties that are still to let!
Rental values do not always match mortgage commitments, neither do they always rise in line with either inflation or mortgage interest rates. They are quite simply market driven. When you rent a property, it is not unlike the retail industry; a shop for example. You have a product on the shelf that should be priced competitively and looks attractive in order to encourage someone to take it to the checkout. Anything over-priced will just sit on the shelf!
One of the most significant changes in Tenant awareness of rental values over the years has been the introduction of property web-sites. On most sites, properties are listed on the screen in rental value order. If your property is marketed too high in terms of rental value, it will be listed next to larger, more desirable properties and stand out as too expensive. Because of these property sites, Tenants have a great deal more knowledge of rental values. Some spend hours researching property values.
If you look at Rightmove (or any other portal site) to assess the value of your property by finding a similar property advertised - REMEMBER - these sites only show properties which have not yet been let. Could the rental value be the reason ?