I felt the same way. The fear and paranoia was overwhelming.
I talked with my fWS about the fear and we came up with plans to ease it.
In the beginning she would send me text messages every 30 min. How much trouble could she get in in 30 min? And if she was, how annoying would it be to have to take a break and send me a text?
She would carry a camera and take pictures with time stamps when she would arrive and leave anywhere she went.
She would show me her phone calls and text and we would compare them to the phone bill to make sure nothing was deleted.
We had a no voice mail rule. She would always answer the phone no matter what. If she was going to be doing something where she couldn't (like a shower) she would let me know a head of time.
Like Itsgoingtobeok said the burden of proof was put on her. At the end if the day, if they are going to cheat they will find a way. But seeing the willingness to do so much to make me feel safe meant more than the proof itself.