Former Home Builder Maintaining a Model Home

This rule was created in HOA's so that one doesn't use their home to "Put a shingle up". That means they don't want members to open up a hair salon or private practice. (Lawyer, dentist, doctor etc...). However, it doesn't necessarily rule out other kind of businesses like Tupperware or other such home based businesses. Those don't generate parking issues or frequent visitors.

Now this situation is a bit unique. Is the HOA under owner control or developer? That was a bit unclear to me. Could there be some kind of arrangement between the 2 builders? Why else would there be a need for a sales/model home if this builder is no longer selling anything? What is their connection to the HOA now as you say they sold out? Is this for other communities they own?

I would look at what your HOA can do for consequences. Just because it's against the rules doesn't mean one can enforce the rules... Meaning do you have the option of liens, foreclosure, or fines in your documents? Do you have a fining schedule? Seems to me once you find the violation ya need to follow up on what you can do about it.