Architect with fixed price without HOAI fee schedule

Hello everyone,

we have acquired a plot of land and are now looking for an architect to design our house. After an intensive exchange of experiences with relatives and friends regarding recommended architects, we met with an architect at the plot yesterday without obligation. After a brief explanation of our wishes and an enumeration of his services, he informed us that he does not bill according to the HOAI fee schedule. He divides a flat fee of approximately €10,000 plus VAT into 3 invoices for 3 "construction phases."

The plan is a "simple" single-family house with a basement and an approximate size of 12x12m. His estimated price for the house was about €300,000 at the appointment yesterday.

After researching on the internet and the HOAI fee schedule, we would have to pay around €25,000 according to HOAI.

It seems possible to us to pay less for the same services.

Do we face any risk or disadvantage by having the architect not bill according to HOAI?

Thank you very much for your answers.

Yes, fixed prices below the minimum rate violate the HOAI and are invalid. But where there is no plaintiff, there is no judge.
Which service phases should be included?

His price estimate for the house is interesting, though. Are those net construction costs?
Two floors or just one plus basement?

Service phases included: Service phases 1-5; partially 7 and 8.
In addition, one could call him at any time if there were questions or problems on the construction site. He would come by at short notice and support with the tasks at hand. According to the accounts of acquaintances, this always worked without problems and everyone was satisfied with his work.

It should be a ground floor with a finished attic, as only one full floor is allowed. Plus basement.

The price estimate was only a rough approximation in a verbal conversation. Nothing that I will refer to later. I am a fan of clear words and no statements like "it always depends on what you want" or something like that. As long as someone builds down-to-earth with a certain degree of luxury (electric blinds etc.) and does not want a gilded toilet, a rough estimate based on experience values should be possible. Based on the construction prices of others in the region with comparable buildings, which have cost around €250,000 in recent years, his value seemed very realistic to me.
He roughly calculated it based on the room volume multiplied by a price per room volume.