if the processing for a house provider is done through an independent brokerage representation,
... then I first have to guess what you actually mean by this question: have you, among the house provider salespeople you have already dealt with, now for the first time met one whose business card shows him as a non-employee?
In sales (in almost all industries) it is common to operate with commercial agents. That means people who do not have an employment contract with the represented company, but a commission contract.
With clarifications like "independent sales partner / agent / broker / representative" it is essentially meant: "this guy is not directly one of us," which regularly indicates that he has no power of attorney.
On the contracts he presents (and on their revocation instructions etc.), it states who you are actually signing with as the real contractual "opponent." Usually, it must then be confirmed by them first.
From the lack of powers of attorney of such a broker it follows that side agreements signed only by him have correspondingly little value. If their content is later missing in the order confirmation of the actual contracting party, you may have to revoke.
Basically, even reputable providers do make use of independent commercial agents – and the fact that these sometimes exclusively represent only this company in this industry does not change their status.
Ultimately, you don't have to care whether the salesperson receives holiday and Christmas bonuses or a fixed salary continued in case of illness. What his word is worth to you depends solely on his status. Only managing directors, authorized officers, and persons with power of attorney can act bindingly for the company. Only parents may sign for children, not their teddy bears :-)
The house provider builds your house, not the salesperson. The contracts and terms and conditions usually also state that the "independent ..." is not allowed to accept payments, etc.