That would have me upset too. Sit tight, gather your thoughts, make notes of everything you want to investigate, take a deep breath and then take the plunge. You could go in for the first time pretending you just spotted the building, checking if it's a pet shop and if they sell food or doggie stuff. Mention that you didn't see a sign.That will give you a chance to check out the animals, and I'm sure if you ask questions the answers will be all lies. But if you do spot something not right, then you should call your local SPCA and report it.
I know it's hard when you have to turn and leave behind the unfortunate animals in there but just maybe you can get the troops together and get some action to close them down ...I think you're right about the pups being from a miller.