I know for a fact the shortest short term stay allowed in Howard County MD is 30 days or more. Renting in Maryland you must have a rental license. If a neighbor or anyone, reports you anonymously or not, a Howard inspector will require you to get a rental license and will require you to not list on the short term rental websites for less than 30 days.
I objected to an anonymous report and stated in the United States we should be able to know who our accusers are and that is not the case in Howard County Maryland. I told the inspector this anonymous reporting is what they do in North Korea, not in the United States. The inspector agreed, he said until the law is changed it is what it is. The inspector said people in Howard County tried to remove the anonymous aspect, but the General Assembly voted it down because the reporting would go way down if the reporter had to make known who they were.
1st hand experience shows in Maryland if someone rents without a license a person can do whatever they want in your property and you don't stand a chance in court. A squatter can stay in your home and you are powerless without a rental license. At minimum you will be required to refund the renter their money. Your lease agreement is void because you don't have a license to operate.
https://www.howardcountymd.gov/Departments/Inspections-Licenses-and-Permits/FAQs
When do I need a rental License?
Every dwelling or dwelling unit in Howard County which is not occupied solely by the owner or owner's immediate family must be licensed. A license is also required if more than one boarder, roomer or renter occupies the dwelling with the owner. This requirement applies whether or not rent money changes hands. Rental Licenses ensure that the Howard County Property Maintenance Code standards are met. The requirement applies to apartments, individually owned condominiums, duplexes, mobile homes, townhomes, hotels, motels, assisted living unit and facilities.
I know this is a real bummer.