I joined simply because this is my field and thought I should chip in, as a non registered user this site has been very valuable to me so I hope this could be valuable to you.
1. Easy, search for providers offering filming. Then confirm filming is available when booking to be sure. Get your camera out straight away before you pay her and if she backs out, leave. Then leave honest feedback. At the point of leaving, most unsure girls will cave if you offer 20 quid more than the agreed fee. Warning: Do not share this footage ever, unless she gives you permission to in writing and you have a copy of her ID. It will 100% guaranteed to come back to you if anyone makes a complaint and the penalties are harsh. Another option is to set up the camera and then record the whole transaction and get her agreement on camera.
2. You can detect cameras easily. Your mobile phone records more of the light spectrum than you see. You need to fire Infa Red lighting into the room. You will see the IR reflection from the lense on the screen of your phone. Try getting your tv remote and pointing at the phone you are videoing with and press a button. You will see the IR light on the phone screen as it happens, but not with your naked eyes. I am sure you will find an app that make it easy for you if you search any app store.