When trying to find an SEO agency, listing the criteria can be very difficult, especially if you don't understand the SEO process. You can contact a good SEO agency in Perth at https://www.totalclicksolutions.com.au/search-engine-optimisation-perth/ to make your website at the top in the search engine for all keyword phrases.
There are thousands of SEO companies out there and with a relatively small number of first page positions, it is impossible to prove their value for all agencies by being on the first page.
There is an unlimited number of reviews you can run on an SEO company. Searching for your company name inevitably leads to listings of articles, directories, and social media pages. There will be some feedback mentioned on the website page if the company is relatively large.
Most online marketing is backlinks, and there are plenty of free tools for checking links to websites. The quality of the websites reflects the ethical standards of that link to their SEO company work.
If you find that an SEO advertising agency has a ton of backlinks that you perceive as spam from other websites, then this is most likely the approach they are taking to market your website, which goes against all basic search engine guidelines. Knowing how SEO companies work on your website is very important.