Burberry Group PLC’s store employees have taken on some new duties: organizing birthday parties, private dinners and art-gallery visits for high-spending shoppers. The British luxury label is expanding its army of so-called private client associates who develop personal relationships with elite customers to keep them coming back to its stores and spending more. Sales growth for personal luxury goods such as bags, shoes and watches is estimated to increase at an annual rate of 2% to 3% through 2020, down from an average of 6% a year for the two decades through 2015, according to Bain & Co. SEE ALSO: Can travel retail save luxury sales? In response, high-end retailers have hit the brakes on store expansion. The luxury industry’s store portfolio grew just 0.4% in the year through July, compared with 5% growth in the year-earlier period, according to data from investment-research firm Bernstein. Many brands are sharpening their focus on collecting data about customers and allocating more space to popular products. Burberry’s store associates view data on past in-store and online purchases by more than 10 million customers with an iPad app. The information on a customer’s size, color and style preferences allows them to offer more tailored advice. Internal figures show that customers who receive personalised services are 20% more likely to shop the brand again and spend 35% more on average. Therefore, brands are pouring more money into training store staff and even revamping their duties.