if you use shapeshift.io it's very safe changer, decentralization system make we can hold our purchasing, so we can manage it, but the rate of shapeshift usually not same like other normal changer.
Well every exchanger has it's own different exchange rate because that was business after all.
If you are really looking into quite safe one to purchase coins, it's not wrong if you will try those exchanger that really proven their names in the market although it's not an assurance that it is 100% safe.
If you really like a 100% safe, you can do some meetups in your location based on party's exchange rate deal.