LONDON (Reuters) -Britain’s antitrust watchdog is investigating Amazon.com Inc on concerns it was hurting competition by giving its own sellers an unfair advantage in its marketplace over third parties, adding to global regulatory scrutiny of the U.S. tech giant. Britain’s Competition and Markets Authority (CMA) said it opened an investigation on Tuesday into whether Amazon’s practices that affect sellers on its domestic marketplace may be anti-competitive and result in a worse deal for customers. “It’s right that we carefully investigate whether Amazon is using third-party data to give an unf…