seeing a lot of comments on the grey area of the illegal apartments, assuming this favors the landlord. I have heard that this in fact favors the tenant.
A: As it is illegal to rent out the basement, the collection of rent is unlawful, and the tenant can countersue for all rent paid to date.
B: The evection process is more complex as it involves squatters rights.
I'm a bit skeptical about the squatters rights thing, however the first one may have some teeth. I have no direct knowledge of these, though I have heard a story circulated in regards to the first one.