Several weeks after listing a seller's home, he and I agreed to terminate our relationship. We both signed a Termination of Listing form (TAR 1410) with the seller agreeing to pay me $400 for the services I rendered to the date of termination. The seller keeps saying he will send me a check for the $400, but he still hasn't. I recently learned that he is selling his home through another listing broker and the closing will take place next week. Should I send a letter to the title company demanding that they withhold my $400 from the seller's proceeds?

No. There is no statute that authorizes you to place a lien upon an owner's home to protect your right to a negotiated fee for termination of a listing. And if you attempt to have the title company refuse to complete the closing of the sale to secure your fee, you could find yourself at risk of disciplinary action by the Texas Real Estate Commission. 

A better course of action is to continue to discuss this matter with your former client. You can also ask the seller's current broker to help resolve this issue. If those efforts are unsuccessful, your remedy lies in filing suit to collect your $400.