I know that sometimes an internet deal comes along that is just too good to pass up, and if someone is on a tight budget and this is the only way they can stay in the game, then I can understand making the purchase. But remember that when it comes time for service or annuals, you are going to have to either pack it up and ship it back or you are going to have to pay an LDS full price for parts and service. After a year or two of this, you will probably burn up any savings you might have made on the initial purchase. Before making an internet purchase, you might want to try taking a copy of the internet ad to your LDS, see how close they can come to the price you have, weigh the difference in price against service costs and make your decision from there. Keep in mind that some equipment manufacturers have a minimum price policy on their gear and the LDS is limited to what it can discount if they want to carry that brand. The way internet dealers get around this is by getting their gear through the "grey market". If you can't afford the shop's price, some shops will let you set up a payment plan which allows you to use the gear while paying for it.
I'm assuming your comparing all online scuba stores to Leisurepro? Leisurepro.com was one of the biggest Grey market scuba retailers on the internet, but they have recently started fixing their prices and selling them at MAP (Minimum advertised price) and are purchasing directly from Distributors. Before purchasing directly from the distributors they did in fact purchase from out of this country, they did not come with a manu. warranty, they did however come with a Leisurepro warranty, which matched or beat the manu. warranty for that product. In this case, you would in fact have to send your product back for service to Leisurepro.
What does this mean exactly? Since they (and almost all online dive stores) are authorized dealers for the products they sell, they do carry a manufacturer warranty, which means, if your LDS carries that gear that you purchased online, regardless of what they say (unless they do not participate in the program), they are supposed to cover your gear under warranty and give you the free parts for life (if your product and manu. offered it at purchase).
Saying, "You purchased that product off the internet, that voids the warranty", that's rubbish and very untrue. Purchasing a product off the internet from a retailer that is an authorized dealer for that product, gives a warranty just like you were purchasing that gear from another dive shop in your city. If asked by any LDS where you bought it, it's none of their business, this is why your asked to register your product with the manufacturer.
As far as MAP goes, this is basicly a way to control the market and not lower the value of products offered, on the internet or in a brick and mortar. However, MAP is not by any means set in stone, this simply states you cannot advertise the price to the public for less than that amount, it doesn't mean they cannot sell it for less than that. This rule doesn't apply to Scubapro, MAP is also their MSP (minimum sell price), there are others like Scubapro, but most online retailers don't sell them because of this very issue (MSP).
I will tell you this, Dive Right In Scuba, the dive shop that I'm currently working with, has a fully stocked online store and we only sell items that we are authorized to sell and any product purchased from our store DOES in fact come with a manufacturer warranty unless stated otherwise. This means you can take that product to your LDS (if they service that brand) and get it serviced.
The main thing to keep in mind, all online stores MUST have a brick and mortar, so they aren't just an online store. You MUST have a brick and mortar to even become a reseller for the big name manufacturers. You will most likely hear someone bad mouth online stores, it's usually the store owner, manager, or uninformed worker/patron.