My puppy is trying to extort treats from me!

My Colonial Cocker Spaniel puppy is just over 4 months old and not doing too badly with learning the rules about toileting. Although hardly a day goes by where there isn't an accident inside. I think it's usually caused by excitement (or sometimes anxiety). She gets very excited when I return home and usually springs a leak then as well.

The method I used for toilet training was to take her ever hour to the designated toilet spot, say "go-toilet" and praise and treat is she was successful. She's now started going to the door when she wants to pee which I thought was a great sign. Recently, however, she has started going to the door and when I let her out she pretends to wee! She will squat for a few seconds, leave nothing by dry paving and then look at me as if to say "where's my treat?". I don't give her treats for pretending.

It's only a problem because I don't know if she's serious about needing to pee and I don't want to be letting her out every ten minutes for phantom peeing in an attempt to get a treat.

Are puppies normally this cunning? Do you think she will stop in time when she realises she doesn't get paid for phantom pee?