Why it matters
A bathroom generates more water vapour than any other room in the house. If that vapour is not pushed outside, it condenses: on the ceiling, behind the tile, inside the wall cavity, and up in the attic. The result is peeling paint, blackened grout, a soft ceiling, mould, and in the worst case rotted sheathing overhead. A brand new $30,000 to $50,000 bathroom with no working fan is a bathroom on a countdown. The two failure modes, in order of how common they are in Canadian homes: 1. There is no fan at all. Very common in pre-1970 homes, where an openable window was considered ventilation. It is not, in February. 2. There is a fan, and it vents into the attic. This is the one that does real damage, because it looks fine from inside the bathroom while quietly soaking the roof structure above it. It is extremely common. And a clock nobody mentions: a bath vent fan lasts only 5 to 10 years. It is the shortest-lived part in the room by a mile. A fan that is running and making noise is not necessarily a fan that is moving any air.
How to spot it
No fan grille visible on the ceiling in any bathroom photo; a grille that is dusty, painted over, or obviously original; peeling paint or blistered ceiling above a shower; black spotting in the corners of the ceiling and along the grout; and a mirror or window that is fogged in an interior photo, which means the moisture has nowhere to go.
What it costs
Properly ducting a bath fan to the exterior, with insulated duct and a real exterior hood, runs about $400 to $1,300. That is a small number sitting in front of a very large one.
What to do
Monitor the finishes. Verify the venting. Ask the agent where the bathroom fans vent to. It is a question sellers are rarely ready for, and the answer matters more than any tile in the room.
Education and triage, not a home inspection. Casaroo can see whether a fan grille exists. It cannot see where the duct goes, and nobody can from a photo. That is an attic check, and it is exactly the sort of thing an inspection is for.