The price of bitcoin via an ATM will always be higher than the market price, I experienced this on my first go and it worked out at a 6% difference, the price you pay convenience I guess.
I have heard of a price premium as low as 6% which to me appears very reasonable. I have never paid less than 8% and have paid as high as 14% (once!). As mentioned above by a couple of psoters, they have to buy the ATMs and maintain them, as well as have someone go around once a day or week to take the money out. It adds up.
On the other hand, it has always been fairly hard for m but better than the ATMs.e to arrange meetings via localbitcoins. Then drive over, spend the time doing the deal and deal with the (very slight in my case) risks. So, a level of 12% is not unreasonable IMO.
Yes, you can get better rates through exchanges, etc. bitcoin.com offers the service for 7.5%, which is kind of high but better than the ATMs. I had used Circle, but they started getting very difficult to use (intrusive as well), even though their premium was something like 1% - 2%.
(USA experiences, once in Canada)