Depends on the situation and how the verbal praise is delivered I think. Not to mention how much verbal praise the dog recieves in general. I pretty much talk to and praise my dog all day long, so if it was going to work as a reward I would have to learn to be less chatty with my dog
She gets praise just for being alive and cute, so how would she know when she did something good
In a training situation I think verbal praise is not high enough value reward. There should be no dubt that it is a reward, and a"good dog" is just not enough when learning something new. But in other settings when the dog does something she has already learned, then a verbal praise will be good enough to reinforce the behaviour in most cases. A "good girl" gets the tail wagging every time so clearly it's valued by the dog.
Sometimes treats are almost in the way because she is having too much fun to swallow so she inhales them and starts coughing. So for anything with speed I prefer to use a toy or myself to reward. Just playing and jumping around and doing stuff she is entertained by. But let's say you are training recall, praising the dog is not going to compete with a world full of exciting stuff. So in that setting praise is a pretty weak reward. A tug toy however...
So I think the important thing is to use different types of rewards for different situations. I do think praise can be a valuable reward. But not nearly as useful as treats or toys
I guess it depends on the dog too, some dogs don't care for food rewards, but I dubt many cockers fall in that category
