It could be that you have just got him and he still does not feel safe to eat yet. dident give him time to settle in.
It could be Cage Temp.
Could be a problem on the inside of the snakes mouth.
could be you are siting there watching him when he is used to feeding when it is dark and or no one is around.."OverNight"
You could try to feed him dead mice..
There are many things that it could be you dont really know unless you own the snake.. hope any of my 2 cents will help