Renting to students is generally not considered a good idea by many landlords. The reason for this is the concern that students usually don't take much care of the rental property they are living in and leave it in a very bad shape when they vacate it. This however is not entirely true.
It's a good practice to make the student renting your property sign an inventory list. An inventory list, also known as schedule of condition, is basically a list of the items present in the house that you are renting out.
It is very common for tenants to request their landlords to allow a roommate to move in. There can be a number of reasons for this request. The tenant might be finding it hard to pay of the rent on his own and wants a roommate so that they can share the rent.