Down payment for a new house? What do you think?

So personally, I would never do that. First of all, I don't understand the whole construct and therefore wouldn't even engage in it. Secondly, €600,000 with 5k net is madness to me. We have a loan of €470,000 with over 5k, and that's already crazy. But it also depends, for example, on whether more children are coming. Overall, we also know too little about you (age, how secure the permanent residence permit is, why you urgently need a house now...).

The real estate agent showed us her own house as a sample, which she built with high quality two years ago. I was promised that our house would also be built with this quality [...] Now we are ready and want the real estate agent to have us sign a contractual agreement. By signing, an amount of €25,000 becomes due, as a flat rate for conversion measures (at the same time also as a down payment). That means the real estate agent is building the house with her own money.

You want to buy a house that still has to be built. The house does not exist yet, so there is nothing to "convert." Whether the developer is professionally a real estate agent or a hairdresser is irrelevant (except that in her role as the seller, in my opinion, she cannot charge a brokerage fee on top of the house price again as a real estate agent). Such a purchase from the developer should include an exposé with a construction service description as an attachment to the purchase contract, so the quality of your house is not based on a shaky oral promise. A reservation fee of about four percent seems unprofessional to me, especially since six semi-detached houses nowadays face around forty to one hundred interested parties. If you as an interested buyer cannot become the purchaser, a replacement will be found within a few hours. Therefore, in the current market situation, she has no marketing default risk (except a self-inflicted one: namely if the construction service description does not convince the banks of the prospective buyers of the appropriateness of the price).

… and anyway: which real estate agent buys and builds themselves, so that they don't earn any commission, which is their income. Hands off!

A real estate agent who thinks she can act as a property developer and needs start-up financing. Normally, payment must also be made turnkey according to the construction progress. It also doesn't fit that you only need financing shortly before completion. Furthermore, there is no guarantee that your girlfriend will suddenly leave. You have a purchase contract, don't get financing, the real estate agent wants money. Property development business is risky and capital-intensive. Find yourself a reasonable business partner and wait until your girlfriend is naturalized.

Now we are ready and want the real estate agent to sign a contractual agreement. By signing, an amount of €25,000 becomes due as a flat rate for renovation measures (also serving as a down payment). This means the real estate agent is renovating the house with her own money. There is also a draft for the notarized purchase contract, which we only have to sign when the house is completed (around April 2022). We will receive the house turnkey.

I don't want to write much, just say one thing: KO criteria for not taking the house are, in your small paragraph, probably a dozen. Essentially: - Down payment €25,000 - Flat rate for renovation measures - Real estate agent renovates with her own money - No description of construction services - No notarized purchase contract STAY AWAY!!!!!!!

Sorry, I probably skimmed over this aspect too quickly earlier:

There is still a draft for the notary purchase contract, which we only have to sign once the house is completed (around April 2022). We will receive the house turnkey.

... and in that respect I also understand the association with "scammers, hustlers, conmen" ;-)
Under such conditions, the house would rather be finished in 3033 or 4044. Read around in this forum a bit using the keyword "payment plan" (they sometimes refer to property developers and sometimes to general contractors, in between you might have to think differently, because with a property developer the big chunk including the land is included upfront, which with a general contractor is charged separately). You will quickly realize: a payment plan in two installments, about 4% before the starting signal and then 96% after completion, that cannot work honestly, no property developer has that much capital or would ever want to tie it up for so long by pre-financing. Either it doesn't work, or it's not above board.

The good news for you is: it doesn’t work (indicator: timing of the notary appointment).

If the notary appointment took place at the beginning (where it would actually belong when buying from a property developer) but the above-mentioned "payment plan" were the same, you would immediately receive an invitation for a talk ;-) from the public prosecutor (due to suspicion of aiding money laundering). You will probably only understand the last paragraph after 1. completing the aforementioned reading session here with the keyword "payment plan", 2. taking a look into the real estate agent and property developer ordinance, and 3. asking a banker you trust to try to explain the topic "Basel" to you in layman’s terms. Only then should it become clear to you that either in the statement that the real estate agent builds with her own "money" the prefix "black-" is missing, or the time until you become suspicious is intended to be used to acquire with your money a one-way ticket to a palm beach country that does not extradite to Germany ;-)