We live in a digital world. We have to assume that anything we do may end up online with millions of viewers. That said, there are limitations. In Oregon, recording a phone call requires one-party concent. Recording video without audio, does not require concent. This includes nanny/security cameras.
It all changes when audio is recorded. The seller (in Oregon) cannot record your showing unless all participants are aware that they are being recorded. This is covered in the state statutes:
2017 ORS 165.540¹
Obtaining contents of communications:
(1) Except as otherwise provided in ORS 133.724 (Order for interception of communications) or 133.726 (Interception of oral communication without order) or subsections (2) to (7) of this section, a person may not:
(c) Obtain or attempt to obtain the whole or any part of a conversation by means of any device, contrivance, machine or apparatus, whether electrical, mechanical, manual or otherwise, if not all participants in the conversation are specifically informed that their conversation is being obtained.
That said, you need to go into every property assuming that you are being recorded, it’s just a part of today’s societal expectations even if it is against the law.
***I am not an attorney. This is my interpretation of the statute.