I have done pre-clearance in TIST. Easy as can be. When our passengers showed up, they drove them over to customs, we taxied over there. Meet the passengers, the line guy walked us all the way through. Gave customs all the forms, didn't ask any questions, stamped the forms, gave us our outbounds and off we went. When we got to our destination which was SFB, we got copies of our forms, gave the orginals to the girl at the fbo and they brought them over customs there.