I've made many purchases from eBags over the years, including luggage, purses, wallets, and accessories. I bought their own brand of packing cubes last year and have been very pleased with them.
Even for items that I don't buy there, I usually look them up on eBags anyway because they usually have good pictures and specs available, and the reviews are often helpful as well.
I've bought from ebags too. Basically, if you know what you want, buying online (at least in NYC) is much cheaper and as long as it isn't some brand that you have never heard of, you are pretty safe. I almost always save money when you factor in the sales tax versus shipping
My big advice is to read a whole bunch of reviews first, and post here for advice. I ended up getting a Sky Train from Redoxx after reading reviews for a few days. Reviews will tell you if the bag meets your criteria - specs on line like measurements and weight are always better verified with independent parties.
Ebags is a great source.