House purchase Baden-Württemberg (early 70s)

The absolute best solution is certainly an expert appraisal of the market value, but there are some alternatives. For example, one can refer to the "local" real estate market report and check if there are evaluations for comparable properties (average price per m² with the same age, similar location, etc.). This is possible free of charge, and the data is based on the sales cases evaluated by the [Gutachterausschuss] in recent years. An alternative is information from the purchase price collection maintained by the [Gutachterausschuss], or more precisely its office; this includes all sales cases from the area of the [Gutachterausschuss], and for a fee, you can obtain information on comparable sales cases.

This provides at least quite good approximations, and the information costs about 100-200€ depending on the number of comparable prices.