gzt:

tardtasticx: The online estimate when I bought the iPhone air said up to $800, and to complete it by going in store within 30 days to complete it. I went to spark today they said the estimate is now $760, but I’ll only get around $500. I asked why, as it’s a great condition phone. She said it was due to the phone not being new in box,

That is starting to sound dodgy and misleading. I gather the online estimator says nothing like checkbox or conditions original box?

Correct - nothing at all mentioned. I think I’ve got the box somewhere but I can’t imagine most people would bother holding onto it. 
If this really is spark (and their “Partners”) policy, then they need their head checked about what a second hand phone should look like and the ranges of their conditions. No one is trading in brand new in box phones.