Property with a price significantly higher than the standard land value

Yeah, that's how it is, don't forget the development. It is often more expensive than the pure area. The standard land value is only a very rough reference value. It says little about the price of the property.

Is it common for the price to deviate (that) much from the standard land value?

Yes, as far as I know, the standard land value is the sum total from the previous years.

Can problems arise in financing if the purchase price deviates that much?

No, as far as I know not. They are aware of the huge price increases. The main thing is that you can pay.

In NRW, the value applies to fully developed plots.

Exactly so, the BRW generally indicates the average price per m² for fully developed plots in this location. However, it is often problematic because there may be few sales cases, and thus the BRW tends to lag behind. Also, problems arise, for example, when nothing is sold there for some time, and then new sales suddenly go for significantly higher prices due to the general market development. People tend to be conservative and do not adjust the BRW to that extent.

It is therefore not unusual for significantly more than the BRW to be demanded; this is due to the problems in determining the BRW, especially in areas with few sales cases.

Can there be problems with financing if the purchase price deviates so much?

A bank once explained to me that only the first approximately 500m² of a plot would be recognized at full value, the rest only at 1/10 of the standard land value, since you cannot develop more area with more buildings. It looks different if you can still divide the plot. Nevertheless, I should have been able to finance a 700m² plot with this bank at the "full" price above standard land value without any problems.

First of all, thank you very much for the further responses. We will visit the property shortly with our contact person from the construction company and will then send the land register excerpt and cadastral map to the financial advisor for review. That should clarify things. But that would surprise me? A property, like a house, also has a market value that is used for collateral. Whether 400 m2 or 800 m2. The question is how this market value is determined. But of course, it may be that a 1500 m2 property is valued differently than 3 500 m2 properties. It certainly wouldn't be in such high demand either.