I agree too with researching his credentials, looking for complaints about him, etc. And if something feels off to you, listen to your gut. you can return his book without having another session.

I'm in the US and my t practices out of her home, but the office is clearly marked with a sign and she also has an "In Session" sign on her door, and there's a hallway that separates her office from the main house (I only know this because I used the restroom one time that's in said hallway). I'd really feel weird about being let in by his girlfriend and her sitting outside the therapy room watching tv.