You should take the expert with you to a second viewing after the first appointment. At the first appointment, the property should initially prove to be definitely suitable for you in terms of location, equipment, and ambiance. At the second on-site appointment, the expert then objectively and independently examines the facts, as already described:
As a case study from last weekend: A purchase consultation in Roetgen near Aachen, an architect-designed house built in 1972 is for sale. The interested party has already visited once for viewing and is seriously interested. The sellers inherited the house, have no knowledge of the property, and want to sell without an agent. During the viewing, an oversized new heating system stands out, which is supposed to heat a swimming pool in the house and is technically nonsensical for use of the house without a swimming pool. It must either be downregulated or even replaced. The house has a high energy consumption due to its year of construction, which should actually be surprisingly low according to the energy certificate. After a rough calculation and examination of the oil deliveries of the last 3 years, about a 1/5 higher energy consumption results. I estimate the costs of an energetic renovation roughly for the interested party and also tell them to the seller/owner. Overall, the owner is willing to grant a reasonable price reduction that takes into account the renovation effort and the possible heating system replacement. I found no structural damage to this house after a visual inspection. I recommended purchasing the house under the negotiated conditions, provided the energetic renovation is undertaken for long-term use.
The purchase consultation has been worthwhile for both sides, as the owners received a realistic assessment of their property for the first time.