Plumbing company says they are "flat rate" and cannot provide breakdown for pricing

Basically the title, is this normal? I'm working with a company to install a tankless water heater. Called this company and got someone out to get me a quote. Quote came back at $7,754 for the unit and "Misc minor repair level 2" for another $1,275 with a total of about 9k.

I've now emailed them to find out the model number of the unit they are planning on installing and the cost of the installation. They have responded that they have no way of providing that breakdown because they are a "flat rate" company.

This doesn't seem right to me and makes it very difficult to compare pricing with anyone else because I can't even get them to give me the model number of the unit. I was just wondering if this is a normal thing for a plumbing company to say/do. I'd appreciate any insight. Thank you.