Have to agree with XXXMgmt. I also like SecureNetShop, it was very easy to incorporate into an existing site and product pages. Customers don't really notice that they are taken to an external store for processing.
And at $79 a quarter, it is pretty reasonably priced.
Plus,it is one of the few shopping cart services that actually keeps data encrypted on their servers. Actually it is the only one that I found when I researched. For most shopping cart services, secure transactions are secure only while data is trasnmitted to and from via a browser. It isn't actually secure on their servers. For some shopping cart services I looked into, encrypting stored sensitive data was a novel idea. (As though servers are never hacked)
As far as offering a shopping cart to customers, I imagine it would be a headache to manage unless the system is simple.