If he says all it needs is to be reset, fine, tell him to get it reset, and tell him to prove to you it’s OK. If he fumbles on this, then you should assume it does not work, that it will not get fixed, and that you will not have an airbag. $1,500 sounds right. There are lots of Miatas to buy, so if this bit of BS bothers you, move on to another car.