Not knowing your website or the platform its built on its quite hard to say. It's a bit beyond the scope of a forum, as you should create a spec for what you're trying to achieve and then pick a review solution that fulfils that criteria.
It's unlikely a proper solution will be based on a plugin though (Trustpilot, Feefo etc aren't). Loox only seems to do product reviews, they aren't listed as a Google seller ratings (brand reviews) partner.
To try answer your questions, for an ecommerce site you'd normally drive brand and product reviews that can be shown in paid ads results and organic results, which is multiple solutions for most review platforms. You'd normally:
- show the brand reviews everywhere for your company; e.g. XYZ brand rated 4.8 out 5 from 500 reviews
- the product reviews show on your product pages/shopping ads; e.g. widget 123 rated 4.5 out 5 with 50 reviews
The reviews are normally called in via JavaScript to display on the website, so show totals and individual product reviews without any filtering. There are ways to filter these on the website (but need a separately setup tool usually). However, in Google Shopping these are shown as is, as they are driven via a feed to the Google Merchant Centre and can't be filtered.
There are some work arounds here though; e.g. you can generate reviews and see how these perform before showing them in Google Shopping, but display them filtered on the website immediately.
In terms of pure Google reviews, these are driven by Google Business, most ecommerce sites/brands will have a Google Business page. You don't have to show a physical address if you don't want people to visit (although you need one to set this up initially, as you get a verification card posted).
If you mean showing reviews in Google ads, you have to get 50 across all products (to start showing in shopping), or usually 100 for brand reviews (to show in search ads). Once you link it to the ads platform, it will show all reviews good and bad, unless you stop using that service.
Drop me a PM if you want more detailed information, I can point you to some cost effective services and solutions, depending on exactly what you're trying to do.