A customer's car warning light comes on, or a tooth starts aching, and they call the first number on the map. Your receptionist is on the other line, the workshop is loud, or it's 1.30 and everyone is at lunch. The phone rings out. The caller doesn't leave a voicemail; almost nobody does any more. They call the next place on the list, and the next place answers.
Most owners know the calls are being missed but not how many, or who they were. The missed-call list on the handset is a row of numbers with no names and no reason for the call. Someone means to ring them back between jobs, gets to a few of them hours later, and finds the person has already booked elsewhere or doesn't remember calling.
After hours it's worse. Calls on a Friday evening or late on a weekday are often the most motivated: a breakdown, an emergency appointment, a homeowner whose AC has stopped in the heat. Those calls hit a closed office or a generic recording, and the business only finds out the next morning, if at all.
The calls are already coming in, which means the marketing worked. The leak is the gap between the phone ringing and someone with the authority to book actually answering it, and in a busy front office that gap opens every time two things happen at once.