A couple questions:
First - (May seem Silly) Was the person you bought from flying the 250 with the DX6i? Personally I would re-bind before I would try to fly or set-up.
Second - Did you get the manual for the DX6i? Again personally, I would go thru the tx and check everything; pitch curves, throttle curves, swash mixes, expo, dual rates, EVERYTHING. The reason I think this is important is because the person you bought from may be a very experienced pilot and have it set up very hot meaning; no expo, high swash mixes for increased pitch and aileron/elevator (roll rate), flat throttle curves, ect. All of these things will make it harder to fly if you are not used to them and you need to know what these settings are so you will be able to check set up on the heli.
Third - Do you have a pitch gauge? Disconnect to of the wires from the esc to the motor(for SAFETY) and proceed to check the heli set-up. You are looking for a level swash, degree of pitch (at center stick, full stick, and low stick) on both blades, ect.
Fourth - I would re-bind again after everything is to your liking.
I know it sounds like a lot but I would hate to hear that you crashed or don't like the way that it flys because something wasn't set up properly.
Damn I write a lot, anyway congrats on the new bird and happy flying!!!!