This is a very professional niche area to argue who/when did what. if it's a DIY, it's even tougher to arrive any conclusion. The previous home owner may never come forward and volunteer anything.
Your realtor will unlikely get involved in such dispute and your home inspector does not cover such in-depth inspection on foundation if there were no cracks that caught his eyes.
You just have such strong headwind against you in proving any fraud.
It may be much more easier to get a professional building engineer to assess the situation and decide how to fix the foundation issue. A few cracks may not tell the sky is falling.
