Whilst Microsoft Commerce Server has been around for a while, it's rebranding as Sitecore Commerce (Powered by Commerce Server) is a fairly recent move. As such, resources are a limited and troubleshooting issues is rather difficult. When developing my solution, I found that as soon as I added a reference to any commerce server dll (CommerceServer.Core.x.dll) I was having a problem with an error "Microsoft.CommerceServer.Internal.ContentListHelper - An attempt was made to load a program with an incorrect format", somehow it was copying the CommerceServer.Internal.ContentListHelper.dll to my application, even though I didn't have a reference to it. Deleting the dll from the bin directory fixed the issue and forced the application to use the 64 bit version in the GAC. However, every time I rebuilt the app, the dll would appear again. Step number three detailed over here did it for me.