It’s not just the owners of brick-and-mortar bookstores who are retiring. Sharon Preiss, who founded Mobile Libris in New York City seven years ago to sell books for publishers and authors at events, is the latest to put her business on the market. Currently, Mobile Libris handles 50 or more events a week. In an e-mail blast to clients, Preiss noted that she will handle all December events and all events that were postponed by Hurricane Sandy that were rescheduled for this year. However, if a buyer doesn’t come forward, she intends to close Mobile Libris at the end of 2012. The business is listed with Mel Lisiten of Lisiten Associates for $249,000.