Well the money would be yours anyways (if you own the machine). When purchasing the BTC at the ATM, you sell some of the Bitcoins you own to the person using the ATM. You can also re-buy the exact amount the person buys on an exchange with your own money. The money the person puts in the ATM becomes your money. Bitcoin has no central authority and doesn't know its price.
Yea, my doubt was if i was buying from an exchange like bitstamp or other.
Since it looks like these machines need to have bitcoins in their addresses, this option is not possible.
What you said makes sense. Thanks for that!