Having tenants can be a hassle, but if the person buying wants to rent it also, that would work out well wouldn't it?
Otherwise if you are trying to retail it to a homeowner, your tenants, in MD, get the "First Right of Refusal". Meaning you will want to have them sign something that says they do not wish to purchase the home themselves. (Or else let the buy it!)
Subsequently, when the house sells, the new owner will be responsible to honor the existing lease.
Getting a potential buyer in to see the place might sometimes be hard if the tenants are difficult, or keep odd schedules etc...by it is usually something that can be worked around.
If by Selling Agent you are mean the Listing Agent than the answer would most likely be YES. It should be someone that is familiar with the area, at least be in the same county. From where I stand I understand the "Selling" Agent to be the one to bring you a Buyer to sell your home to. In this situation they sometimes come from all over, sometimes even from another state.
Good luck. Please let me know if I can be of service to you.