Background: Off market property with a $10k delinquent tax lien.

Situation: Agreement with seller to pay them the 10k to cover the lien and pick up the property via seller financing.

Question: How can I structure this sale so the seller doesn't run off with my 10k? I was under the impression that the deal woudn't close until the lien was cured, which means seller would receive 10k but then would have to use the money to cure lien before deal can proceed... 

Thanks folks.