In the external database system I store the following information about my customers:
(1)The SL (Second Life) Agent "USERNAME": It is the name that you choose when registered (created) your SL account. And it is also the one you use when logging into SL.
(2)The SL "UUID": It is a 128-bit (16 byte) used in SL gris to uniquely identify each SL account. The UUID is generate automatically in such a way as to make collisions (matches) unlikely. In other words there not exists 2 different accounts with the same UUID. As Data Type a UUID is represented as a string of 32 hexadecimal characters with four dashes interspersed. It is used primarily to identify avatars within SL grid.
The UUID IS NOT the User "PASSWORD" that every SL Agent/Resident needs to log into their Personal SL account, and into the SL grid. It is (SHOULD ALWAYS BE) a private information. Indeed, I will NEVER ask customer for their PASSWORDS (In the same way I do not share mine !!!!). The combination "USERNAME" + "UUID" is enought to identify my customers to deliver them product updates.

Providing an online "Front-End" at "https://www.buzzthespianvirtualworlds.com" where customer will find usefull information about my products: Documentation, User-Manuals,...

In this regard, I adhere to the common practice with most of the Second Life merchants; and the answer is NO. Each sale is bound to the Second Life Account with which the User did the purchase; since the money is charged to that Account's linden balance.

As a way to provide Second Life residents with an opportunity to taste a weapon before purchase it, a special version of it is available free of charge (0 L$).
In my store vending machines click the "DEMO" button to get one.
The DEMO version has all the same features as the standard (For Sale) version, but with the following differences:
1) ONLY Weapon (i.e. Sword...) and its HUD are provided (Sheath IS NOT included).
2) The "UPDATE" feature is disabled in the DEMO.
3) The DEMO product has a limited life-time: ONLY 1 Hour (60 minutes) since your first attachment.
4) Take adventage of your DEMO time from the begining, because detaching it before consuming the DEMO time, will    disable the weapon after a second attachment.

As part of BTVW T.O.S. FREE UPDATES (free of charge!) of products are made available.
Update Checking IS NOT performed automatically (i.e. after attaching the weapon), instead it is done from the weapon HUD, clicking on the "UPDATE" button.
You can find on my Website, whether an update for some product has been released, in the product information web page.

BTVW also provide a "REDELIVERY" service for products.This means that any Second Life Resident who purchased any of my items, can get the item RE-SENT (Forwarded) again.
To request a redelivery, just visit my inworld store an click on a "Redelivery Terminal". Then you will sent a URL back, open the chat window and click that URL. To open it in your computer web browser.
The page will show you a gallery with all your purchases. Click "REDELIVERY" button for the item you want to be redelivered.
NOTE 1): You will receive the same item version you purchased.
For updates please read the "About Product Update Service" faq.

"Double-Purchase" refers to the action of chosing to pay for an item you have alredy bought before. My Web-Based sales management is designed taking this in account, and when any Second Life resident purchase one of my items (by clicking "BUY" button on one of my vendors), the system search a database, and in the case that the item was previously bought, the vendor object is inmediately notified of such event and is instructed to refund your money.
So now you can sleep with no worries, since a "Double-Purchase" done by accident just CANNOT happen.

I am starting with a store in a small region, focusing on Melee weapons.