The hundred-to-five-hundred foot rule and what it means here
Ask why a rat problem keeps returning after a good trapping run and the answer is usually distance. A Norway rat forages between one hundred and five hundred feet of wherever it sleeps, and at Baltimore's density that circle takes in a stretch of buildings, the ground between them and every container along the way. So the animals you catch indoors are drawn from a pool that is not yours. You can empty your share of it in a fortnight and have it topped back up from a burrow four doors down that nobody has looked at. This is the mechanism behind the familiar complaint that the rats came back, and it is not a failure of the traps. Two things follow. First, exclusion becomes more valuable, not less, when the surrounding pressure is high, because it is the only part of the job that does not depend on what the neighbors do. Second, the outdoor half of the work needs to reach past your own wall: burrow openings in soft soil, runways worn through ground cover, and the bins and enclosures that keep the population fed. With 43 inches of rain a year keeping vegetation heavy, cover you clear in spring is back by late summer, so treat that half as maintenance rather than a one-time chore.
Two species, two different sets of repairs
Maryland gives you the Norway rat and the house mouse, and a plan built for one will not stop the other. Rats are ground animals. They dig, they follow walls, and they enter where the building meets the earth: under a door with too much clearance, through a rotted basement window frame, at a utility penetration nobody sealed, or through a gap where old mortar has crumbled. The repairs are heavy and visible, which is why they are also easy to verify afterward. Mice are a finer problem. A quarter-inch gap is enough, and the gaps that matter are inside as much as outside: the hole cut for a supply line under a sink, the space behind a dishwasher, the seam where a chase runs from basement to attic. A building can be rat-proof and still be full of mice, because nobody went back for the small stuff. The practical takeaway is to ask which species a quote is written for. If someone has found rat burrows outside and fitted door sweeps, that is good work, but ask separately what happens to the interior penetrations. Those are cheap to close and they are the difference between quiet and almost quiet.
Shared walls, multiple units, and who fixes what
In a building divided into units, the person who notices rodents is frequently not the person who can authorize the repair, and sorting that out early saves weeks of nothing happening. Animals in these buildings travel vertically. A basement entry serves an upper floor within a day, because pipe chases, boxed-in ductwork and the void behind a stair connect the floors without opening into any room. That is why a tenant upstairs hears activity while the source is two floors down. Sealing a single unit accomplishes very little in that arrangement. If you own the building, treat the whole structure as one job and start at grade, where the animals actually get in, not at the unit that complained loudest. If you rent, your job is the record. Photograph droppings with a visible date, note the room and the time of night you hear movement, and keep every message you send about it. Then ask for something specific: the basement door swept in metal, the window wells repaired, the trash enclosure secured. Naming the repair moves the conversation past whether traps were set, which is where these discussions usually stall.
What to expect from the walkthrough
You can judge a rodent company in the first hour by where it chooses to spend time. If nobody leaves the room where you saw the droppings, nothing useful has been established yet. The exterior circuit is the part that matters most in Baltimore. Someone should be looking at ground level for burrow entrances in soft soil, at the clearance under every door, at the condition of window wells and sills, at each place a pipe or conduit passes through the wall, and at where water stands after a storm on a lot sitting only 33 feet above sea level. Standing water is a map of where digging stays easy. The basement is the second stop, because that is where the foundation, the framing and the utilities all meet, and where droppings and rub marks record how long this has been going on. What you should have at the end is written and specific: which openings exist, what closes each one, where traps go, which dates someone returns, and what is deliberately left out of the price. A quote with no punch list attached has told you the cost of something you cannot describe.
Reading two proposals that look alike
Rodent quotes tend to resemble each other on paper and differ enormously in what actually gets done. Compare the work before the number. Start with the physical repairs. Does the proposal name openings and the material used at each one, or does it list exclusion as a single line. Only an itemized scope can be checked when the crew leaves, and only an itemized scope changes the building. Then the follow-up. How many return visits are included, what triggers an extra charge, and what the provider does if activity restarts in six weeks. A trap plan with no dates is a hope with an invoice attached. Third, the exterior. If there are burrows or a shared bin area, an interior-only plan cannot hold, however competitive the price looks. Ask whether rodenticide is planned, where it would be placed, and how pets and non-target animals are kept away from it. The cheaper figure in Baltimore is very often a monthly station service that leaves the structure untouched. On a block that keeps resupplying, that is an expense with no end date, which is the opposite of what sealing buys.