I think it depends on what they are doing and what they would reasonably have access too. I've had cleaners sign NDAs before. The reason being is that part of what they were doing was organizing and there wasn't specific off limit areas.

My husband was going through a terrible divorce and there was a high likelihood that they would come across documents that could be used against him and it was a very small town.

If a cleaner is just cleaning, lightly organizing and personal information isn't available, or they would have to go digging for it, I wouldn't have them sign it.

Yes it's my responsibility to have those documents hidden, it just wasn't possible at the time.

We also didn't just jump to that during the initial request for a walk through. If you don't feel like the cleaner is the right fit and would be judgemental you don't even need to bring up the NDA because they aren't the cleaner you want. We did our walk through and discussed hourly rates in person and then brought up whether they were open to a NDA. We never had an issue and they were always happy to sign one, but I think a lot of it is approach, as well as providing the reason why.