For the purpose of?

Venting? Warning? Praise?

Something else?

It appears that the dead website that @rotmulaaginskyrim@programming.dev mentioned was not much more sophisticated than what @sub_ubi@lemmy.ml suggested, “federated reviews”.
https://web.archive.org/web/20220411192056/https://www.exitreviews.com/

Nothing is stopping you from creating a Lemmy community for general product/service reviews, but I doubt it would work very well nor be very popular. But ActivityPub-based federated reviews sounds like an intriguing idea. I don’t know if/how ActivityPub can handle structured fields (https://web.archive.org/web/20220608160103/https://www.exitreviews.com/submission), and you’d probably want a search system that leverages those fields.

NeoDB

https://neodb.net

!neodb@lemmy.zip

There used to be a website called exitreviews.com but it redirects to looria.com now, which is an actual company and I can't tell if there's bias or not.

It used to be intended for reviewing any product (usually upon failure).

federated reviews

Another one of the million projects in my backlog that I'll never get to.

There's one major problem with this kind of website that I've been wanting a solution for, and it's that people often only leave reviews when they have an exceptionally bad experience. So when you see a product with lots of negative reviews, does that mean it's actually bad? Or is it just a very popular product, so lots of people will find issues with it? I think the solution to that is some form of review pre-registration. When you buy something that's intended to last a while, inform the review website of that purchase. Then if something goes wrong and you leave a negative review, you can see what percentage of purchases are affected.

Make a community for it? Or maybe an instance? @federatedreviews.com

Make a community for it! I'd subscribe.

Not sure where you're located,but we have https://www.productreview.com.au here in Australia. I've occasionally found it useful.

I don't know, unfortunately. This reminded me that I used to occasionally read product reviews on epinions.com, which was apparently was taken offline in 2018. It was basically what you're describing. Another proprietary website bites the dust and loses all content. :(

I heard about neodb.social recently, which is for entertainment media and is popular in China (although you can post in any language). Seems like we need something like that, but without specific product types in mind.