It could just be a case of giving the dog more time blueboy. I had a terrier cross that wouldn't chase a rabbit but it wasn't long before she turned on and then there was no turning back.
What the lads are trying to say is that it's best to see the parents work, if possible, when you are buying a pup as then you'll have a better idea of what you are buying into. If I wanted a pup to bring on for terrier work, then I'd like to see the parents do the work in question. You've bought a pup from what sound like parents who work a line with beaters so you've taken a bit of a chance when it comes