What is the pragmatic benefit of -let's say a bank, since you mention them- in having ready-made child chains? What's the advantage of them over, for instance, a data base?
The big advantage of child chains is that you dont have to take care of bookkeeping yourself anymore. This task is outsourced to ARDR stakers. Bookkeeping usually produces costs (including security costs) and therefore reduces profits. If the cost for paying ARDR stakers is lower than doing the bookkeping yourself, there is a clear benefit.
... the possibility anyone has to return and be refunded when the purchase something they are not satisfied with when they try it. ... A Smart Contract, since it would be irreversible, has no place in such economy.
In your examples you assume that a token is used as medium of exchange between the seller and the buyer of a good. Why should the seller not be able to give back the token to the buyer, when the buyer is not satisfied with the product? The trade will happen under a certain legislation. If the buyer knows the identity of the seller he can just take legal action. If the seller is a machine the buyer should know exactly what he gets, because a machine cant do otherwise than it is programmed. But even in this case a refund would be possible - by the creator of the child chain. If he is a machine too, well, then the buyer doesnt expect a refund possibility in the first place. Maybe I am even discriminating machines by implying they are not capable of doing a refund...
What Smart Transactions in Ardor mean is just that the creator of a child chain can determine which ones of a predetermined set of transaction types will be possible in his chain. I dont see how this makes refunds impossible.