You could make an offer with the request that the seller either repair the foundation or pay to make the foundation repair with the lowest of 3 bids from contractors with a license.
If I'm going to own and maintain a property for a long time, then I want to take ownership of solving any problems with it. I'm the one who will be dealing with any ramifications for a long time.
I would get some estimates for repair and negotiate with the seller based on those and then fix the problem when I close.
If the wall hasn't moved too much, there is a process where they can use carbon fiber strips adhered to the wall to keep crack from moving. That solution requires no digging. It can be pricey, but I believe they will guarantee the foundation won't move.
Another option is to dig holes outside the house, and bury anchors. Then drill through the foundation and connect to the anchors and use those to make sure the cracked wall doesn't move.
Many times the reason a foundation cracks is from pressure created from water freezing and thawing. So, you may also want to do some work outside the house to dry the ground nearer to the foundation.
@Kevin Sobilo beat me to it.... Yes if you are going to own this property than you should own the repair. Don't chance it to having the buyer have a friend-of-friend perform a half-hearted job. I would recommend getting estimates and leveraging those to offer a lower asking price. If it turns out the juice isn't worth the squeeze, than emotionally detach yourself from this one and move on.