Yes, not only is it a used piece of equipment, but also it was returned by the previous owner because something was wrong with it. Onkyo then fixed it and is now allowing ecost to resell it (more than likely with the same warranty that normally comes with a new model).
This is what the word "refurbished" means in the item description "HT-S760 6.1-channel home theater audio system Refurbished by Onkyo".
This does not mean that you should completely avoid refurbished items. Some people has had great success with them. You should simply be aware of the risks. Before buying, you should feel that the savings are considerable and that the Manufacturer's Warranty is worthy (dependent upon the manufacturer, some refurbished items are given a new warranty even longer than one of their brand new items). On this item it appears you have to email ecost for exact warranty information.
I noticed that ecost also offers extended warranties with on-site service. This might not be a bad idea on a refurbished purchase (dependent upon the cost).
As far as the reputation of ecost.com goes, here is a link to the bizrate.com site:
It appears they have had more than 50,000 reviews and have a 95% Satisfied Ranking (90% Positive & 5% Neutral)! Seems pretty good to me, but you can read some of the reviews for yourself!