There is another trick, especially used by developers who build several terraced houses etc. at once: They specifically set up a GmbH for the contracts, whose business purpose is solely the sale of the properties and completion of the project. The company presents itself to the buyers as a normal experienced local construction firm, but the contract is with this GmbH, which, as soon as the acceptance has taken place, essentially acts only as a mailbox company until it is dissolved one or two years later. 5 years warranty? No way, because your contractual partner no longer exists. Any assets have long since been transferred to the parent company via a profit transfer agreement or even paid out as salary to the managing director (the latter less likely due to tax reasons).