Since the notices are now here:
The field staff member was very nice and, due to Corona, also offered to handle everything over the phone. Various data are queried, such as own occupation, previous construction experience, used vacation, etc. These data affect the calculated hours in the BG-Bau program.
What remains completely open, however, are the data of the wife (how much vacation, part-time or full-time job, children, etc.). Also, the house is only roughly distinguished by type of construction (timber frame), size, etc. Even after the conversation, BG-Bau does not know which floor covering (simple laminate or tiles) was installed by oneself, whether the walls were wallpapered/plastered/painted, whether I have a simple electrical installation or a KNX system, etc. If parts of the trade were carried out both independently and by companies, it is up to the field staff member to make flat-rate deductions from the hours again. He did not really look at the invoices I had emailed in advance either, as he had to read many explanations from me first.
In the end, he said that according to his program, about 300 helper hours must have been incurred more than I had reported, but that I would be off the hook with a later report of about 200 hours. I then asked what would happen if I did not submit a later report. The internal office would probably check everything again in detail, and in most cases, the hours would double again.
For my electrical installation, there was then another questionnaire, as this was almost completely done by a friend. More than 20 questions were asked about the connection between him and us. Since he carried out and planned the work independently, had his own tools, and could access the construction site at any time independently of me, he was classified as an entrepreneur-like activity and could not be insured (so no BG contribution).
By the way, the employee is also monitored by BG; he always had to press a stopwatch when we talked on the phone.
The calculation and the whole procedure are therefore very arbitrary. I will pay and let the matter rest. Considering the actual helper hours worked, somehow still a good "deal."