That's a fair concern. StayThere only indexes listings from established PMSs like Guesty, Hospitable, Lodgify, and Hostaway. In many cases, those listings were originally imported from Airbnb or other OTAs when the host joined their PMS, which then created their direct booking website and distributed those listings across additional channels.
StayThere doesn't change the regulatory status of a property. Hosts are still responsible for complying with the local laws and regulations wherever they operate, just as they are when accepting bookings anywhere.
So unlike an open marketplace where anyone can create a listing, these properties typically already have an operating history. Longer term, I want to surface additional trust signals like open-format Q&A, years hosting, reputation metrics, and more reviews where available, so guests can better judge whether a host is a safe bet. Some PMSs also aggregate OTA reviews onto their direct booking sites, allowing that reputation to carry over.
Depending on the security of the sites you link to you might be able to show them locally in an iframe so users are only redirected if absolutely necessary and you can give an easy way back to search results/landing page