It is recommended to have a structural engineer evaluate the stability of the house in this situation, as the inspector has noted an issue with one of the I-beams not being anchored to the outside wall. The age of the house, 30 years, and the presence of three posts supporting the house may not be sufficient to ensure stability. The fact that the I-beam only goes halfway across the basement and the other I-beam is anchored to the cement wall on the other side of the basement could indicate a potential structural problem. It is important to address any structural concerns identified by the inspector before purchasing the house to ensure the safety and integrity of the building.
It's best to have a professional structural engineer evaluate and repair any structural issues in your home as they have the specialized knowledge and experience to ensure the safety and integrity of the building. Although, you can certainly try to do some research and gather information to understand the problem and its possible solutions, but it's important to note that addressing structural issues requires a high degree of technical expertise, and if not done correctly, it could lead to further problems down the road. It's also important to comply with building codes and regulations which can be hard for a non-professional to navigate. My friendly advice is to trust the professionals to handle this type of job, it will save you time, money, and ensure the safety of your home.