I wouldn't distrust the dealer yet. Yes, down a quart would read around the low mark on the dipstick, but our dipsticks are temperamental from my experience. How long did you let the car sit before checking your oil? The tech might've topped you off anyways even though you said not to.
Obviously theres lots of reasons for consumption. I always thought my car was consuming oil through the pcv system. But I didn't really realize until recently how common it is on our cars for the spark plug tube gaskets to go, or at least it appears common after searching. Found that out when I went to do my plugs the other day