EBay can be great if you do your homework on prices. Large stores (even B&H) will sell overstock or old stock in the hopes that someone will pay as much or more for the convenience, particularly if they live somewhere away from big centres. I bought a ton of Aquatica stuff, for example, that B&H purchased from Nikon, when they stopped being the Aquatica US distributor. They couldn't sell it as new, so I got some great deals on dome shades and gears, that were essentially new. You also have to be really careful about grey market items and warranties. Many US and Canadian camera representatives, such as Nikon, and Canon, won't work on non-US equipment, in order to protect the local distributors, even though it is an item they made. (I think this is deplorable: how do they know I didn't buy it overseas?) So, if it's new stuff, check that it is from the US, if you're a US resident, and covered by the warranty. Often, that is why there is a price difference. Companies like B&H carry both US and "Import" models. Avoid 3 day sales on high end gear: they are suspicious, and I sadly speak from experience. There is fraud still out there. Check not only feedback, but what the person has sold previously: have they sold camera equipment before to satisfied customers? Often fraudsters sell a bunch of cheap junk to set up positive feedback. The guy that ripped off me, and lots of other photo buffs, had been selling small ticket used stuff on EBay for two years. Look for those that have been members a long time.
If there's only a slight price advantage, go with the reputable company, instead, as shipping costs are often inflated on EBay, and they are known for standing behind their products.
Cheers,
Marli