If it was captive born, I would expect the seller to know the breeder, know that it has been eating and what it has been eating, and have a better "clue". Sounds to me like it was farm raised and sold as CB. Very misleading in my opinion. No disrespect to your friend, he was probably "told" the same thing he is telling you.
First, get it out of that aquarium and into an appropriate enclosure. Check out this link for more information regarding "appropriate" enclosure:
http://www.finegtps.com/cagingbabies.htm
You need to maintain its temps around 85-86 degrees and humidity during the day around 70-80%, allowing it to drop at night slightly (humidity, not the temps). The temps for a baby should never fall below 80 degrees. You will want to use some type of overhead heat source controlled by a good thermostat. Good luck trying to maintain these environmental conditions in that aquarium.
Meg is right, it needs to settle in before it will eat (most of the time). Not only will that tank make it nearly impossible to maintain the right conditions, the clear sides exposes it to too much around it and is probably stressing it out, hence, it isn't perching like it should. Get it into a smaller tub or tub-like enclosure and put it in a room that has little or no activity. Make sure you are providing a day/night light cycle. Also, and I am sure this crossed you mind, do not handle the animal! Their spines are very delicate and can fracture easily. Quite often, you do not know a fracture occured until it gets older and develops a kink. Until it is about a year old, it needs to be display only; however, don't put it on display. (room with little activity, remember).
What you have there is not like your typical corn snake or king snake. Forget most of what you thought you knew about snake husbandry. They require very specific conditions to thrive. However, when you find a way to meet those conditions, they are not difficult to maintain. These animals are truly a joy to keep but it is imperative that you do the research and heed the advice of experienced keepers. Check out the website I provided regarding husbandry in my first post. It offers a great deal of valuable information. If you feel like spending the money, his book is a good investment; however, his site alone has enough info to get you started. Besides, your next big purchase, IMO, should be a good thermostat.
Priority right now should be getting it into a better enclosure. Once this is accomplished, you can concentrate and getting something in its tummy. This is also not going to be like feeding a corn snake but one hurdle at a time.
Good luck,
Bart