Britney Spears enjoyed a whirlwind shopping spree in Miami on Sunday. The singer opted for some retail therapy just 10 minutes after checking in to the Four Seasons Hotel before her performance at Miami's Mansion nightclub.Britney and a group of friends hit the shops in South Beach and their first stop was a 15-minute visit to No Lines Tanning.The 'Toxic' singer then treated herself to some Guess? jeans, tops and shorts. A source told People magazine: "She bought quite a few things. She left out the back of the store - she seemed happy."Britney also tried on several corsets and mini-skirts at The Mosh Pit and was happy to browse around the store with other shoppers.The source added: "They asked if she wanted the store closed, and Britney told them she was OK and not to worry about it. She tried on several micro-mini skirts and bought a $180 hand-painted pink corset by Kimikal. She liked it, bought it and wore it out of the store."Britney then dashed to Mansion for a 7pm sound check and left the club at 9pm for some last-minute shopping.The 25-year-old splashed out more than $1,500 on dresses, shoes, belts and accessories at The Atrium Miami Beach. Meanwhile, her Mansion performance failed to impress some audience members at the weekend. A source told the New York Post newspaper: "The crowd sneered at Britney's hideous white go-go boots and ratty hair extensions."Madonna's brother Christopher Ciccone was particularly scathing of Britney's outfit choice. He reportedly said: "My sister would never go onstage looking like that."