If you have a genuine sitting tenant there are a number of problems you will have to overcome before you even consider selling your property. A genuine sitting tenant is a tenant who has been in the property for many years without a tenancy agreement. This could be a very difficult situation as the process to evict these tenants can be extremely long, extremely costly and more than anything a very big headache.
If you have inherited a property that has a sitting tenant, who happily pays rent but will not sign an agreement then it may be worth while trying to negotiate with them. If they want to remain in the property and are happy to pay rent then taking that step to enter into a tenancy agreement really isn't such a jump. Many cash buyers, like ourselves, are happy to take on a property that has a guaranteed rental income per month.
If the situation is not so clear cut and the tenant is causing a problem then your first step should be to contact a solicitor who will be able to tell you how the whole process will work.