My company and I are building a new system for a relatively large client. We are going to be replacing their entire system, which includes some eCommerce aspects to it among many other things. It is not a typical public shopping site, and there are many things about the system (both back end and front end) that are quite different.

Some of the people I work for are convinced that we should be using a third party product to implement the eCommerce pieces (shopping cart, catalog management). Their opinion is that it is a solved problem, and we shouldn't have to reinvent it. Given that direction, I have reviewed around ten different .NET based eCommerce platforms, and I struggle to imagine how we will be able to smoothly integrate any of them without a lot of friction. They are so all-encompassing that I feel like they are probably better suited for implementing simple shopping sites rather than larger systems that happen to have some eCommerce aspects to them.

We have a really nice architecture planned for everything else (Entity Framework, ASP.NET MVC, etc.), and my gut is telling me that trying to introduce a third party platform will cause unnecessary fragmentation and difficulty.

I would love to hear some opinions from people who have been there. Have you used a third party platform for eCommerce? Was it a typical shopping site or something different? Did you feel it was a help or a hinderance? Thanks.