Legal Question in Real Estate Law in California

Well, "recourse" means legal recourse which by definition is either suing or at least the threat of a suit. He could sue for specific performance, rather than damages, but it sounds like the seller cannot perform even if ordered to, because he cannot deliver clear title. If the seller cannot pay off the lien there is little your son can do as far as "recourse." There are, however, a large number of details implicite in your question that you have not provided, and could not reasonably provide in this kind of forum. In those details may be creative options, including forcing the seller to use other resources to clear the lien, or working with the bank to buy at foreclosure.

If you do not want to take title subject to a lien, you do not have much choice. It appears that the lien has been discovered during the escrow, and you asked for title to be cleared. If the seller won't clear the lien himself, then you have a real problem. You most likely can't sue for fraud, because you have not suffered any damage, other than aggravation, as the sale has not been completed. You could sue for specific performance, but would still have to take the title subject to the lien. I would have to review your actual purchase and sale contract to let you know if a failure to deliver good title was a breach, or a failure of conditions.

If your son had completed the purchase before discovering the lien, and the lien didn't show up in the title report or public records, he might have acquired the property free of the lien as a so-called "bona-fide purchaser for value and without notice."

My first though upon reading the question was "Why the heck does he want this property so badly?" Looks like he's proposing to pay more than it's worth.

Maybe bidding at the foreclosure auction is his best alternative, and he may get a lower price and it will result in a lien-free trustee's deed, but remember that bids must be paid in cash or near-cash form acceptable to the trustee.