Almost all the Rescue Organisations are the same when it comes to returning a dog. If you let them know about it they will not give you a dog.
I would begin by making a list of the traits you DO want in a dog. Go wild - see what feels right and what you truly want. It will give you a pretty good indication of what will work and what you need to avoid. (This includes character traits, looks AND disposition, i.e. dominant, submissive - toward both dogs and humans, etc.)
The problem with Rescue dogs is that they almost all have some issues. Some are easy issues to deal with, others not so easy. As much as I understand your wish to get a rescue dog (my first one was a rescue) it is not for everyone because of the baggage that some of these dogs come with and the difficulty this CAN pose in training them.