I think the money will be refunded only after 90 days of commercial launch and not after preview offer is over. So one has to further continue for 90 days with commercial services before one can opt out. There must be some catch which purchaser should clarify or read the security deposit refund terms properly. Because normally some amount gets deducted (30% or 50% or 10% etc.) if you apply for refund before the days specified in terms.