Trust rank is a new concept (not quite new) from Google. It is similar to page rank, but it doesn’t works on the usual algorithm of page rank. But it is popular that people have started to work to develop trust rank. It is not easy to gain trust rank as getting a page rank. For getting a page rank you simply need quality links from sites. In addition to having links from ordinary sites, if you have edu text links, it will be considered more valuable.

 
So for building trust rank Google considers your domain age, for how long it is registered, does it have a SSL certificate etc… Apart from that Google considers your site trust worthy if you have an edu site linking to you. This is because edu sites can only be owned by institutions or universities which are valid and are limited when compared to other domains such as .com or .us. This is because .com domains can be registered by anyone who have money to pay, but to own a edu domain he needs valid papers which only a university or an educational institution has.

 
The basic thing about trust rank is, Google assigns a parameter which decides how much your site can be trusted. So if the so called edu sites link to you they are pretty sure your site can be trusted. So the easiest way to gain trust rank is to get edu text links to your site. But it is not as easy as it sounds to get an edu link. This is where text link sites come handy. They offer high PR edu links at reasonable prices. So don’t waste time and grab their packages.