Contract clause for subsequent purchase price adjustment in the new development area

I don't know the property. So one can only speculate here.

Smart on the seller's part, I would find it fair. Of course, you can also already pay the land price for your garden...

It would almost be worth considering whether that is not the better deal. Because whether the general inflation even remotely matches the land price inflation in the next 20 years is doubtful.

Smart of the seller,

By the seller, but for both sides.

Of course, you can also gladly already pay the building land price for your garden...

That would be the alternative. As planned, the improvement must only be compensated upon its occurrence, thus sparing the buyer’s credit line for now. The OP can be glad and grateful that a professional here considers aspects that would otherwise have completely escaped the homeowner builder in their consumer thinking. Or did the OP think he could make the profit on the Rhine crop rotation alone?

My personal advisor says that a corresponding clause is common practice, so it is unlikely to be illegal. The question is how likely its occurrence is.

My personal advisor says that a corresponding clause is common practice, so it probably isn’t illegal. The question is how likely its occurrence is.

One can actively participate in this. Attend every relevant municipal assembly and oppose the reclassification into building land. File an objection.