1. Does the source code provided include full source code of libraries and can anything be customized by an ASP.NET developer ?
The base purchase of AC7 includes all code-behind and page source code. It does not include the core CommerceBuilder API code however it is available separately for purchase. I've been modifying AC7 since Beta 1 release (5 releases ago) and have yet to require the purchase of full source code. What is included with the base purchase of AC7 is more than sufficient for massive development and modification of an AC7 storefront.
2. For ASP.NET developers which have already customized the ablecommerce shopping cart software, what do you think of the design and architecture of the application. What about the documentation, scalability and ease of customization ?
That's alot to answer

Design and architecture is fantastic. Able fully implements strongly-typed data classes for every single component. Once you wrap your head around the core design concept, you'll see how remarkably well designed it is. I've yet to write a line of SQL code - it's just not necessary. Since you get a TON of source with the base purchase, there's plenty of live code examples of how to accomplish specific tasks.
Documentation from a user perspective is great. Documentation from a technical standpoint is still a work-in-progress. Able just went Final with AC7, so the majority of effort was spent getting user documentation ready. Technical information is available but it could (and will) be improved. Honestly, once you look through the forums you really won't need technical documentation. The data classes are really that well designed.
Ease of customization is a hand-grenade. One developers "easy" is another ones "nightmare". A system this large and this complex must be designed from a specific perspective. Once your development mindset comes into alignment with how Able did things, you'll find it's extremely easy to modify and customize. The heavy use of .Net user controls makes this even better.
3. Is it possible to customize the product catalog trough the administration to make some products available only for a defined customer role or do we need to implement that ?
No, it is something that has been discussed and I believe is planned in a future release. For now you would have to customize your install to implement such a feature. You can trick the system by assigning certain products to specific warehouses so a purchase cannot be made without the correct group membership, but product visibility would still be for all visitors.
4. Is it possible to have a customer with multiple user account with different rights (for example with a supervisor who is the only person which can validate the basket) ? If we need to implement this is the system flexible enough to allow these type of changes
All user accounts are based on the email address as the login. As long as different email addresses are used, you can leverage the AC7 custom-written role-provider security to limit access to specific admin menu options or functions. You can further enhance the security by manipulating the web.config permission settings provided in the various Admin folders.
There is no "basket validation" in AC7. I'm presuming this is an internal procedure unique to your organization.
5. Is there a Service request functionality (contact us, ticketing service)
There is a basic Contact Us page however it does not have email functionality. Able has posted a quick user control that adds email functionality. I have written a more robust user control and is available for sale on my website
http://www.AbleMods.com.
No RMA or ticketing system is available at this time. My next for-sale project is a full RMA add-on system that includes proper stock management and refund/credit handling. I am planning on starting development next week and expect a beta to be available by late November.
6. Is it possible to have a call center account which can create customers and take orders for them ?
Since all security is based on login user email address, you just need a separate email login for your call center account. At that point the account could easily be assigned a specific order-taker role with limited permissions on the admin side. This should be easily accomplished without modification.
I hope all that helps. The community here in the forums is second-to-none. The vast majority of posts get a response within an hour, very few go more than a day. Lots of tips, helpful topics and even whole modifications are available and free to the community. I've posted several useful business-related articles as well, you'll find those in the Helpful Topics forum. Able also has a Wiki that provides some great reference material as well as very technical documentation.
For the price and the flexibility of a full .Net implement, you really aren't going to find anything better from a developer perspective. Is AC7 perfect? Of course not. But if you have good developer skills, there's really nothing you cannot do with the storefront. I've got AJAX rotator controls, integrated Google Maps into product pages, flyout menus etc. It's kind of fun discovering something new you can do that you didn't realize was possible
