Go get the dog, you have been nice enough. If a man is not going to keep up his part of the sale go get your dog. Just my thoughts
Until the dollars exchange hands the dog still belongs to the original owner! Also I have a uncle who has a back injury over a year old and he still moans and groans in pain to get up or sit down so I would have to think the buyer isn't gonna be using the dog any time soon. If buyer is a friend I might be a little more chill on the deal but if it was a person who I had no previous knowledge of the dog would be at my house after the 2 week trial was over.