All of the dogs I've ever gotten I've gotten from a shelter. I can recall choosing one dog over another, and my reasons were varied. I do recall seeing dogs that looked like they had shut down or had something wrong with them. Now with being a shelter volunteer and doing Facebook crossposting as well, I know what the shut-down look is: Fear, confusion, loneliness, homesickness, worry, and a lack a hope.
Here is an example:
Please consider taking in a shelter dog. Dogs are social animals. With a little cleaning up, they recover so nicely.