There is no golden number when it comes to link popularity, but generally speaking, more is better. It's good to take a look at the competitive landscape when it comes to link popularity, because this will give you an idea of how many backlinks it takes to establish your site as an authority site in your industry. Fortunately, there is a simple way to find out how your site fares against your competitors in terms of link popularity. All it takes is a simple search, using an advanced operator:
Go to Google.com and type the following in the search box: link:http://www.yourdomain.com
In Yahoo you'll use the same advanced operator in your search: link:http://www.yourdomain.com
You've probably noticed that Google is reporting significantly less backlinks to your site (and your competitor's) than Yahoo. This is normal, as Google does not report every backlink that their spiders have indexed, whereas Yahoo is much more open to sharing that information. That's okay because this still gives you a good idea of how you stack up to your competitors. If your competitors are beating you out in the search engine results, and if you find that they have an abundance of backlinks whereas your site does not, then it's time to get busy building your link popularity.
Link farms are websites that were created simply to farm out backlinks. The website owner might offer to place a link on their site to your website for a one-time or ongoing fee, or it may even be free. Not all purchased links are bad-What sets a link farm apart is the lack of quality content on the site. Link farms often have little to no valuable content, they are just simply webpages full of backlinks to a wide assortment of totally unrelated websites. Many of them will also have ads displayed all over the page. If you see a website that offers free or paid backlinks, explore it first to see if it contains content that is useful, and related to your website. If it's just a page of links that point to an array of sites ranging from tobacco sites to sites about scrapbooking, you don't want your site to be associated with it. Well, unless your site is about how to scrapbook with tobacco leaves.
You should accept only if it makes sense for you and the sender to become link partners. You don't want to exchange links with just anyone, you're looking to build links from quality websites that contain content that is relevant to your site. Do some research before you accept: