Always always always, calculate the price they are giving you before you decide to trade. The centralized exchanges that will custody your coins often have better pricing. Just don't leave anything significant on them. I leave only dust. The internal market is the safest way to trade HBD for Hive, you may get less than some centralized exchanges. Shop around.
Update: I just read your post. When making trades use only limit orders. The internal market uses only limit orders. If you put a market order, orders can be cancelled new prices can be put in before you execute your trade. With a limit order, you can attempt to buy from the books and if they do the same thing the trade just starts waiting for them to restore their orders to the price you set or until some other user creates a limit order that matches yours.