I'm going to take a shot at this, but keep in mind, I'm not nearly as articulate as you when it comes to critiques. You are the master! So I'm going to give you my honest opinion. (I'm also a fan of your art so please don't take this the wrong way)
You have the essence of this beagle down, he/she does look like the photo. And your skill as a watercolor artist can't be denied.
This piece sort of reminds me of an illustration that I would see in a children's book, not a bad thing, but not something I would personally look for in a pet portrait.
Maybe the dog needs more depth or color variations. I think the eye needs to be looking forward and have less or no white around it. I don't know if you're a dog owner or not, but if you can see the whites of their eyes, they're a bit freaked out!
Kudos to you for launching into custom portraits, it appears to me you are trying to hard to duplicate the photo. I think with some experimentation you can nail this and make it your own!
The cat portrait is much better, you must be a cat lover!
http://www.etsy.com/listing/121031345/winter-special-original-pet-portraits-in
