Selling rental properties offers up some different challenges than selling most other types of property.  We usually find ourselves dealing with tenants because the property owner wants to offer the property for sale with the tenants in place.  Doing so, or trying to do so, continues to produce income for the current owner.  From the REALTOR's perspective, we would actually rather try to sell it either empty, or with the owner living in it.  It is so much easier to sell that way, from our perspective--showings are much easier to get set up and we aren't dealing with tenants who don't want the property to sell.  Many times, tenants make it very difficult to show a property for several reasons: they are paying a lower rent than market rents and therefore don't want the property to sell; they just don't want to move at all because they really like living where they are and they're fearful that the new owner may ask them to leave; etc. 

If you own a rental property, I always advise that you to speak with the tenants first BEFORE putting the property up for sale.  You want to work to get their cooperation in getting your home sold, if at all possible.  Ask them if they have an interest in purchasing the property.  I've had sellers receive pleasantly surprising answers when they ask this question, the tenants are, in fact, interested in buying the property.  However, if they aren't, work with them on how the showings will be set up, and offer them some type of incentive to work cooperatively with the REALTOR working to sell the property.  These incentives can vary widely, from a discount on the rent, letting them out early from their lease, and any other incentive that you can come up with that works for both you and the tenant.  I had one seller give the tenant a gift card to a local restaurant that he knew the tenant frequented.  He gave him this card to have dinner there for the times that the property needed to be shown during either lunch time or dinner time.  I thought this was a very creative idea! 

Always keep in mind that the goal is to make it as smooth and easy to get prospective buyers in to see the property as possible.