iPad trade in value

I bought a new ipadPro, cover and pen for $1500+ at an Apple Store and was told that the trade in value of my old iPad Pro was $150. I needed to transfer an ID app from the old pad to the new one, but was told that I could do the trade in within 2 weeks. So I returned after 10 days, but was told that now the worth of the old iPad was $105 which is all I got. I was not told that there might be fluctuations in the value when I first had the iPad appreciated and it doesn’t feel fair that somehow the worth went down 30% within the two weeks I was informed I had to do the trade in. The people in the store were sympathetic to my ’ frustration’, but that doesn’t adequately describe how I feel about this