After doing a little research on the topic, I found an interesting code provision in Frederick County, Maryland's Code of Ordinances regarding pest control.  Apparently, pursuant to Section 1-6-45(d), an owner may be liable for performing extermination services prior to renting or leasing a structure.  The burden shifts between the tenant and the owner depending on the number of units.  

The Code states, "[t]he tenant of a structure containing a single housing unit shall be responsible for the extermination of any insects, rodents or other pests in the structure or the premises," but for larger properties "[e]ach owner of a structure containing 2 or more housing units shall be responsible for the extermination of any insects, rodents, or other pests in the structure or on the premises except where infestation within a housing unit is caused by a failure of the tenant to take reasonable action to prevent the infestation within the housing unit."

Are owners typically familiar with code provisions of this nature?  Just one more compliance measure that investors must be aware of.