Odd Hamster Behavior (anger, instability)

Question
My roommate and I bought a female, long haired teddy bear hamster about a week ago. The pet store advised us to leave her be in her new environment for a few days, and then try to pet her and let her smell us and talk to her so she can get used to it. So far, she runs from us, has bitten my roommate several times, and hisses anytime we try to pick her up to clean her cage. I'm very concerned.
She also seems to fall/tumble... a lot. In her hamster ball, in her cage... she will literally fall with her rear up over her head.
She's been carrying her food up a tube to another location and keeping it there. I am under the impression that this may be a sign of pregnancy.
The time is running short for when we will be able to return her to the petstore, which, at this point, I would prefer to do. I would like someone a little tamer, but I'm also a little concerned they will hurt her rather than put her back on the shelf.
Any and all help with this matter are greatly appreciated.

Thank You,
Katie

Answer
Heya,
  Untame hamsters are a pain. but its important you keep trying to handle her and not just ignore her. take the top of the cage and start by just holding a treat in your hand for her to come and get, after doing this a few times put your hand in front of her to sniff and pick her up gently round the tummy and put her down. she just needs to learn you are no threat to her. keep trying the same time everyday. the best time to handle your hamster is when she is fully awake and her ears are fully open.
 for more help on handling use my site www.angelfire.com/jazz/hamsters
  Storing food is normal hamster activity, in the wild they would search for food at night and store it up to eat during the day.
  i'm not sure about the clumsiness, it may just be she is not used to the ball/cage yet.
  If you take her back to the shop you will have to ask what happens, usually once a hamster has been taken from her brothers and sisters its difficult to return them becuase once they've been taken away they can become very territorial. you'll have to ring and ask the shop what happens.
  if you do want another hamsters you're best off getting a longhaired male, as i have found they are always friendly.
  keep trying, and good luck!  
~Suzi