There is something called the "grey market". It is a methodology that marketers can use to get products at less than wholesale and sell for a lower retail. In general, it violates most mfg's policies and does not allow the retailer to offer warranties. I do not want to go into the details of how the process works, but it can involve illegal acts or acts that are in violation of commercial contracts.
If the retailer cannot sell you a product with the mfg's warranty, be wary. Many will offer their own warranty and the quality of the warranty work may be poor. In addition, one usally cannot take advantage of local repair facilities. For example, there is some Nikonos equipment sold over the net or by deep discounters that does not come with Nikon's warranty--just the warranty of the retailer. If you have trouble with the product, you cannot get warranty work done by the extensive network of Nikon-approved shops; you have to send the product back to New York, etc. That can be a pain.
On a positive note, I have bought things via phone from Performance, Inc. of Chapel Hill, NC and have been very satisfied with the products and the service. Also have used Berger Bros. for photographic items and have been extremely pleased with them.
However, in general, I purchase things from my local scuba shops because I want them to stay in business. I have found that the difference in price--when all the shipping and handling, returns, etc. are taken into account--is small. And, boy, do I appreciate being able to stop by to get something two or three days before a trip.
Happy shopping!
Joewr