TheSearcher: The carts are in all probability made by an Org-sanctioned, Witness owned company, who will show their "appreciation" to the Org for putting business their way.
And that is the 64 dollar question:
Who is making the carts? Which JW company is it that is supplying the carts and making money from it?
Nice gig if you can get it - guaranteed sales, just have the WTS tell the congregation that "Jehovah" has told them to buy his chariots. After all, the WTS doesn't even have to sell them for a profit - that little item is taken care of when the Society men visit the manufacturing plant and shake hands with the JW who owns it.