When it comes to hognose even the largest adult female will have too much space in a 40 gallons breeder not too mention the difficty of providing proper temps
To start of at 12 grams you want something no bigger than a 6 quarts tub sometime there is even a need for something much smaller, 10 gallons is still too big
As far as care the info is out there there are various datasheets.
As far as question you want to make sure to ask about feeding and here are the things to avoid.
Do not buy an animal that is feeding on scented preys.
Do not buy an animal that feed on live (finding live pinkies is very hard and would get old quick)
Make sure the animal is well started at least 10 meals on unscented and 10 meals on frozen, those are the minimum I would expect especially for a new owner.
More and more you see new owner buying hognose that feed on scented or may have had one or 2 f/t (sellers are in a hurry to move them) and it's a big mistake, because if your hognose does not feed for you, you have very little room to get them back on track due to their small size.