Everyone who has ratings does it. I used to rate 3 = professional and fully acceptable until I got a call from Dell asking what they had done wrong, and then from Honda. I realized ratings are all inflated and staff are effectively penalized for less than perfect, and since I'm not going to screw someone because I disagree with their rating scheme, I just set 5 to acceptable and go off that.
The sane way to do it would be to ask yes no questions, but that would require thinking.
Nearly every time I have a bad experience with a company the problem is systemic, but a bad rating will be associated with the random person who served me. So I don't participate. If the problem is particularly bad I find another supplier.
If they did their job, I'll give them the "you did your job" 5 stars.
Even if the company has systemic problems, they still need to pay bills as long as they still have the job.
Finding another company is a smart option. I'd also write to the management to explain why that problem is blocking you from doing business with them, without mentioning who you spoke with.
The sane way to do it would be to ask yes no questions, but that would require thinking.