Source: personal experience of closest friend taking a friend as a "temporary" housemate and being driven to despair when it quickly became obvious temporary meant semi permanent in reality. Following that, I gave the same advice as I've written here, to 2 other friends considering "helping out a friend" with a room, and in each case the outcome was along the lines of "thanks, I didn't know how to say no, and I didn't see the problem down the line". That first case, the friendship was destroyed by the incident. The other 2 it survived. But how to.say it is as important as what to say - to know how to.set boundaries and draw lines. I've learned that as part of an open lifestyle where boundaries and communication are critical, and use the styles described almost daily as needed, they work very well.