Alexa.com (Alexa Internet) is an internet company which provide information which now owned by Amazon. Alexa provide information about quality traffic of a website or blog. Alexa had a system which called Alexa Rank which not become one of an indicator which really important and can be a measurement of a website or blog quality.
Alexa rank had a judging system based on rank 1st, 2nd, 3rd, etc so smaller the number a website have, it have a better rank based on Alexa and it shows that website have quality, good, and trustworthy. For example for now www.google.com have the 1st rank based on Alexa
To know what the rank o f a site in Alexa, you can directly judge it from the site www.alexa.com and enter the site that you want to check, or you can directly use add-on or Extension on your browser.
Download Alexa Sparky for Firefox
Alexa Internet’s free Firefox extension! Alexa’s extension accompanies you as you browse, providing you with Alexa data about the sites you visit without interrupting your browsing.
for Chrome you can use Extension : Alexa Traffic Rank
The Official Alexa Traffic Rank Extension, providing Alexa Traffic Rank and site Information when clicked
For online businessmen, Alexa Rank is one of the measurement which is really important when you want to promote your product, and for other internet users, usually reference from Alexa is also important, where we could now are the site which visit for information is the good one or not.
Based on my opinion, sites which can be trusted to do online transaction is a site which have rank under 10K, and a sites or blog which have rank under 100K are the category of quality site which often visited by lot of people and have quality information and content