Online travel agent Opodo seemed to offer the best deal when Des McGhee searched Kayak, the price comparison website, for a flight from London to Glasgow. Until he reached Opodo’s checkout page, that is. The price had more than doubled, from the £116.80 quoted for four tickets with easyJet to £242.80, with £126 of this the cost of checking in four bags at £31.50 each. It wasn’t until he received the booking confirmation from easyJet that he discovered that the…