There are a few tests you can do to assess the dog's behavior in the shelter. All following tests are taken from the "Meet your Match" dog character assessment guide by the American Society for the Prevention of Cruelty to Animals.
First of all, ask if the dog was tested for aggressive behavior. It's not your job to test for (read: provoke) aggressive behavior in a dog you don't even know. This should be standard procedure when receiving a new dog (shelters don't want their customers to be bitten), but some shelters might not do it by default or might not know how to do it properly. Ask if the dog displayed any problematic behavior while housed there.
Next, ask if they have a room with video surveillance. This will be needed for at least one test. Have a ball and a second toy (like a plushie or tug toy) in your pocket (your hands must be free).
Ask the shelter if you may be monitoring the room with video surveillance.
- One staff member should bring the dog into the room without speaking to it.
- The staff member should leave the room without interacting with the dog.
- Wait for 4 minutes.
If the dog stays at the door for the whole time, maybe even scratching and whining, it probably has separation anxiety. If it freezes or hides away, it has some other form of anxiety.
Bad manners / social anxiety
After the time for the first test is over, enter the room and greet the dog in a friendly voice. Keep standing straight up for at least 2 minutes (no bowing down, crouching or sitting down to interact with it). If the dog jumps at you, scratches you or forcefully bumps into you, it has bad manners that are hard to train it out of.
If the dog runs or hides away when you enter the room, has it's tail between the legs, avoids your gaze and doesn't approach you for 2 minutes, it has social anxiety.
Get the prepared toys into the room and start playing fetch with the dog. If it doesn't want to play fetch, play with the other toy. Play very enthusiastically for a minute or two, then abruptly stop playing and hold the toy in your hand. Do not speak to the dog and do not pull the toy away, but move it with the dog if it continues tugging it. Stay passive for 2 whole minutes or until the dog loses interest in the toy. If the dog still tugs the toy and animates you to play after 2 minutes, it is toy addicted.
Keep in mind that these tests cannot find all problematic behaviors or signs of abuse. They just uncover the most severe problems. The smaller problems are just as individual as abuse can be, but most of the time they are not so severe that you as the owner cannot work through them. A honest talk about the dog's behavior in the shelter can be very informative, too. And don't forget that dogs can change their behavior once they are in a different environment.