I am starting a price comparison website of a niche product category. when I go live I want reviews of the products and the vendors to exists. I see a lot of reviews on yelp and other review sites, how do I import these? Is there any method or do I have to contact each of these review sites?
moreover is there any widget/tool/api for including new reviews that users write? or should I consider parsing the reviews?
Thanks in advance
It's a bad idea to build a business around other's content.
If you are doing this in small scale, your site would risk being banned by Google for too much duplicate content.
If you are doing it big, you'll risk getting notice from Yelp and probably get sued.
You don't have copyright of the content thus you can't use it beyond "fair use". The copyright of reviews in Yelp belongs to the users who submitted them, but there should be some agreement that only Yelp can use it and can handle the copyright issue on behalf of the user.
There is a similar discussion in Quora: http://www.quora.com/Web-Scraping/What-would-be-the-implications-of-scraping-Yelp-reviews-for-the-purpose-of-providing-local-businesses-with-better-sentiment-analysis You can see Yelp only provide very limited result from API. The reviews are their treasure, they'll use every methods to protect them.
Are you looking to partner with other review sites, or simply find a way to lift their content and use it as your own?
If the former, you'll need to contact them all and ask if they have affiliate or data-sharing agreements.
If the latter, good luck... There are ways to do it, but it is unethical and can (will) get you in trouble in various ways.