I have seen a lot of sites using this URL structure:

webapp/wcs/stores/servlet
webapp/wcs/stores/OrderShippingDisplayView

What application is it? Lots of the competition of my client sites use this in their sites.

IBM WebSphere Commerce

The application is IBM WebSphere Commerce, a Java based application. Very powerful application, but obviously for enterprise companies, so that means your customer must be ready to shell out some big bucks. I'm not sure if you can offer this directly to your customer though, or if you need to become an IBM certified partner. It offers call center, sales center and complete warehouse distribution control; amazing software. We use the application - has multi store, multi language and multi development team country office based systems. It starts around £100,000

Updated

You asked about justifying the software. I don't wish to sound rude but this major eCommerce software and may be out of your price bracket:

Gartner Magic Quadrant - the world famous ecommerce tradeshow marked the following eCommerce platforms as leaders:

IBM WebSphere Commerce
ATG Commerce (Oracle)
Hybris

Their criteria for selecting eCommerce companies:

• Has at least 50 production customers for e-commerce functionality, each with at least an average of 10,000 transactions per week
• Has at least five new referenceable customers for e-commerce in the past rolling four quarters, and five referenceable customers that have gone through at least one version upgrade of the application.
• Has generated at least $5 million in revenue for e-commerce in the past rolling four quarters.
• Has demonstrated active market participation, including, but not exclusive to, inbound customer inquiries to Gartner customers and prospects.
• Has multiple production references (a minimum of at least 10) on a current version, and visible efforts to sell and/or market product to new customers.

On top of that the price can be justified by the fact that it is IBM branded software.

• It supports mobile checkout without mobile and table themes.
• Offers kiosk systems so for people in the company stores around the world. All goes into one global database with analytical for business.
• Call center and sales center with multi lingual systems for tracking and handling customers and trade customers (B2C, B2B)
• Offers multi development features for multi office, multi language and multi stores
• CDN and advanced load balancing with SSL and multi domains and DNS rapid fast delivery
• Warehouse and distribution integration with multi chain and multi chain commerce

(Note: these points, this is about the eCommerce partner not the client, so it says that IBM or Oracle should have at least 50 active production customers who use their software with at least 10,000 tps per week). I was surprised Venda Ecommerce was not mentioned since Boohoo.com/Gorgeouscouture.com gets around 4000 orders per day.)

And much more. There should be a wiki on questions like this. WebSphere Commerce is enterprise driven, it is for enterprise companies and the £100,000 figure is not even the cream on top - let alone the cherry. On a positive note they now offer the following versions:

Versions (6, 7, 8**)

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Express (low) (version 7)
Professional (mid) (version 7)
Enterprise (high) (version 7)
Cloud (high - enterprise only, new for 2012) (version 7 and 8 ***)
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6 ** WCS 6 is an obsolete environment now and organizations are actively encouraged to upgrade. 8 ** not released see WebSphere Commerce 8