If I used a bitcoin ATM that stands in a public place and something went wrong during my transaction for example power outage or for any other reason,and I lost
some bitcoins, who will be accountabie. Will it be the shop owner who rent the BTC ATM or the owner of the Btc Atm.
For every malfunction, be it ATM or coffee or soda vending machine the company or individuals that owns the machine are the only ones that can reimburse you.The shop has basically no control over it, they are just earning either a flat fee or a percentage of the sales.
Besides any modern ATM (at least traditional banking ones) have a small battery that would eject the card and print the error code on a receipt in case the power failure or if the connection to the bank server is lost.
But, because of the fees I would advice against using an ATM to buy bitcoins, other than one time to satisfy your curiosity.