(ShareCast News) - Stanley Gibbons' sales for the first half of the year are expected to be flat and profit is expected to take a hit, according to a trading update which sent shares plunging on Tuesday.The AIM stamp and collectable retailer reported progress was made in completing high value sales in the six months to 30 September. Sales for the period were at a similar level compared to the previous year but gross margins and profits are expected to be substantially lower.The company said the outlook is positive, with the group's auction calendar more heavily weighted towards the second half of the year, and expects to return more revenue and profit as a result.At 1509 BST, shares had dropped 40p (27.87%) to 103.5p per share.