4 Month old veiled is perfect. If you are going to a place that has the whole clutch there, stay away from the small ones. It is a survival of the fittest. You want to look for a larger of the clutchlings (Note: just because they are small doesnt mean that there is a problem or not healthy. depends on the breeder). As said before, Check the eyes to make sure they are not sunken in. If you can get the cham to gape at you check the inside of the mouth. There shoulndt be any mucus or anything like that in there. Limbs should be straight. There should NOT be fecal matter around the vent area either. Ask Cham specific Questions: What do you feed them? Do you suppliment/gutload (should be yes, if no, go somewhere else)? What do you suppliment/gutload? What type of lighting do you use (Should have some sort of UVB)? How do they Drink water (If they say a bowl, walk out. Should be misting and drip system)?
Hope this helps, Good luck with the purchase. I hope everything works out and you get a nice healthy Cham.
Frank