By Yeawon Choi SEOUL, July 30 (Reuters) - Seoul shares slipped by midday on Thursday because of worries over the earnings outlook for coming quarters after some disappointing results were released for the April-June period, with shares in market heavyweight Samsung Electronics down. The Korea Composite Stock Price Index (KOSPI) was down 0.2 percent at 2,033.89 as of 0238 GMT. "Local shares have priced in lukewarm earnings for the second quarter, but investors are still worrying over