I wonder if it wouldn't be more beneficial for this discussion to happen between you two so that people navigating this forum for support don't have to read pages of two people's chat.
I currently do not use QBI but reading what's going I find it extremely difficult to support the notion that nobody can make changes/improvement to a mod that is released here.
Yes, I know you have a commercial version of this for CRE Loaded, osCommerce, etc. but I am assuming this version you released for Zen Cart is released under the same licensing as Zen Cart and it's open source? If that's really the case, can you really say people cannot make changes to "your core?" Again, working under an assumption that might be faulty.
Please keep in mind that the very code/mod you're trying to protect is useless if Zen Cart doesn't exist for you to be able to touch the core and change the Zen Cart code or integrate with it. Your mod is Zen Cart QBI which means it needs Zen Cart and QuickBooks to be of any use not the other way.
I completely understand your concern about people messing up code, not providing good documentation etc. but I think the Zen Cart developers also deals with same issue. If the Zen Cart team will take the same approach, perhaps nobody will actually be able to release a Mod because they would have protected their code too much to allow anyone to make changes.
On the contrary, there is actually a section on the forum dedicated to posting more efficient code of doing what Zen Cart already does. They are soliciting people to post code changes as way of welcoming improvement.
All Microsoft products as well as the big software manufacturers are subject to people posting work arounds, code update, security holes and fixes, etc. publicly and there really is nothing any of these big company can do about it other than use that to improve their next release.
I don't believe that Merlin was in any way trying to disrespect your wishes. His suggestion is a better approach for those that want to keep up with upgrading their Zen Cart. The more mods that are released that takes full advantage of Zen Cart system to minimize users having to touch core files the better we will all be in the end.
I want to thank you for releasing this mod. You have done a great job! Clean codes and superb documentation. I know that similar mod I have looked at in past cost $100s so this is a great gift to the Zen Cart community and your commercial version is extremely cheap compare to other solutions available out there.
Hope I did not offend you with my post in any way as that's not my intention.
Happy Zenning!