Cost for house, external dimensions approximately 7x8 m, 2 full floors

Guys, the HOAI is mandatory! If an architect makes flat rate offers below the minimum rate, this agreement is invalid. That means if there's ever any trouble, he can pull this card ...

Wow, is that really the case? Because yesterday I saw an offer from other acquaintances. They are building something quite comparable but have a flat rate that's only half as high as our offer! That's quite tempting...

If it ends badly already. Same story as without a contract, demand payment according to [HOAI]. It also always depends on your counterpart and your behavior in the existing business relationship.

[*]the offer we have received now has no itemization, zero details and only the indication "Costs according to cost estimate" and then the sum of 325,000;
[*]based on that, a fee of 53,000 is calculated; but we will never hire an architect for 50,000
[*]as I have now learned, the basis for the offer calculation only includes items 300 and 400; whether this is also the case for us? no idea. so the 325,000 could be massively too low
[*]If I understood correctly, the basis for the calculation is net. Is that also the case for us? no idea? If yes, the gross alone is already approaching 400,000

What I still can't figure out:

[*]If the 325,000 euros are the eligible costs and
[*]If they are correctly stated as net and
[*]If we assume that the total costs are 50% above the eligible costs,

then our small semi-detached house with its good 100 sqm costs well over 500,000 euros. That is all absurd...

Yes, you need to have explained to you where this amount comes from and how/whether the fee adjustment will be agreed upon if this amount is not reached.

In addition, you can ask acquaintances who have used the inexpensive architect whether they also commissioned service phases 1-8 or if any services were excluded.

You can also ask the potential partner how often he will be on the construction site. I have received answers ranging from "when an appointment is scheduled" to "daily." The latter certainly involves more effort. Site supervision and documentation (service phase 8) account for 32% of the fee... if you just sit in the living room, that's rather easy money, possibly at the expense of quality.

I think we paid almost 50k in fees for service phases 1-8 back then when we were with an architect, according to his specifications. However, the total costs were about 550k. So somehow that seems relatively expensive to me.

Just a side note from me, because much has already been said and we also built with an architect.

We started with a budget of 200k (house + incidental building costs), after visits to several architects we ended up at 250k. In the end, it was 330k. And the garden is not even close to finished.

And I think the argument "self-inflicted" to dismiss "no time" is wrong. I want and have to take that idea away from you, even at the risk of becoming unpopular.

It is your damn duty to deal with it. Either yourself by investing time or by money. If in doubt, more money than you like. A "I didn't know because I had no time" does not interest any judge. Cf. ignorance of the law excuses no one.