"PS there was no mortgage."

Not for the initial purchase; for this: "2019 John Smith, John Smith Revocable Living Trust (seller) did a Intrafamily Transfer and Dissolution changing deed to John Smith, My Client (buyer)."

There is either a sale or a gift.

It doesn't matter what your client knew or didn't know or was surprised. That is extraneous to the situation, because it has no impact.

As pointed out, you need to legal documents; then, follow the timing. So far, it seems there would have been a Gift Tax issue in 2019, and there is no step up in basis. If your client is the only name on the deed since 2019, he uses the basis given to him.