It finds only posts, not comments. That's a good thing. Comment karma accounts for a comment's entire content. What if the comment gets upvotes for something other than an Amazon link inside it? Post karma is a bit better in this respect.
Reddit Search supports any domain. So you can search any shop. Like vat19.com and etsy.com.
Reddit allows browsing by domain. Like https://www.reddit.com/domain/amazon.com/top/
Secondly, some subreddits are specifically devoted to product recommendations:
* https://www.reddit.com/r/shutupandtakemymoney/
* https://www.reddit.com/r/IdBuyThat/
* https://www.reddit.com/r/AmazonTopRated/
And Reddit has a JSON output: https://www.reddit.com/r/shutupandtakemymoney.json?sort=top&...
[1] https://www.reddit.com/search?q=subreddit%3Agadgets+site%3Aa...