It is always advisable to seek permission from the companies before using their online reviews for research purposes. Some review sites, such as Tripadvisor and Yelp, have specific guidelines in place that researchers must follow when collecting and analyzing data from their sites. These guidelines often require researchers to obtain permission from the review sites before collecting or using any data. If you are planning to use reviews from these sites for research, it is recommended to contact the companies directly to seek permission. In your request, be sure to explain the purpose of your research, the methods you plan to use to collect and analyze the data, and how you plan to ensure the privacy and anonymity of the reviewers. You may also want to consult with your institution's research ethics board or IRB to ensure that your study is ethical and in compliance with any relevant regulations.

Thank you Ajit for your detailed response. I am struggling to find a way of contacting the companies at the moment, so that is my current task. It is my ethics panel that require I try and gain permission, so I am hoping that other researchers who have gained permission may have some guidance on who to contact. Your suggestions of points to include when I do make contact are very helpful, thank you. I had mistakenly assumed that reviews would be classed as in the public domain and it would therefore be appropriate to just cite and reference their origin.