Technically, properties can be--and often are--sold without having satisfied the various liens in all 50 states. Each state approved contract (or an addendum/rider in some cases [as in OH and a few other Midwestern states]) that contains a clause about the buyer buying the property subject to various pre-existing liens. The CA state approved contract contains that clause.
Having stated all of that, what would happen will depend upon several factors (including the actual lien[s], the current market value of the property, etc).
If the property you're trying to buy has an IRS lien against it, there are companies that can help the seller get it removed. My wife and I bought a short sale home last year and just before we were due to close the IRS caught up with the sellers and put a lien on the title of the home. It stopped the sale of the home in its tracks.
Bob Crane at Ameritax.com was who helped us. It took several weeks but he worked with the sellers and title was able to be perfected so that we could close. If you have any questions about something like this, let me know.
If you are referring to a Lien placed by a Contractor, for example, the Lien would have to be satisfied before the Property could clear Escrow.
When there is a Lien, it is referred to as a Clouded Title.
The Seller is responsible and that is the reason for the Title Insurance.
For more details, you can talk to your Title Company.