Can dogs tell the difference between when we are unable to do something for them, versus being simply unwilling?

A team of researchers at the University of Veterinary Medicine Vienna, working with a colleague from AS University of Applied Sciences in the Netherlands, has found evidence that suggests dogs, under some circumstances, are able to understand the intentions of people that they do not know. In their paper published in the journal Proceedings of the Royal Society B, the group describes experiments they carried out with treats given to a variety of dogs.