Viator is owned by TripAdvisor. I have probably booked with them for 30-40 excursions, all of which have worked out perfectly. It's important that you use their website or app, though, and link it to your email. That is how they communicate. Viator also has a lot of "Reserve Now, Pay Later" options that eliminates the risk of not getting refunds when you cancel (which also has to be done at least 24 hours before the scheduled tour). Your cc does not get charged until 24 hours before the tour, so cancelling is always hassle-free. I have had several cases where the tour operator communicated an issue to me through Viator which resulted in me cancelling the tour.