Well, when selling stuff most people want to know that you are not selling a box filled with bricks. So you probably at least need to open the box and take photos of what all is included inside. This will also show how complete the unit is (for example, is a keyboard included with it?), and if it is still in good physical condition (heat and humidity can damage an item in a box).
Some people do like items in unopened boxes, but those are usually Apple nuts.
Off hand I'm not aware that there is anything special or desirable about Tandy packaging.
Do Tandy 2000s have any kind of clock battery that can leak? If they do, you may need to open up the unit and document the internal condition.
As for powering it up: Meh. You would need its keyboard, a monitor, and appropriate software to really test it. So if you don't have those or are not knowledgeable in those areas then all you could say is the obligatory useless "it powered on and the fan spins".
Anyway, congrats on finding a Tandy 2000. Those are absolutely collectible.