I think Gazelle used to be good but they were so overwhelmed with iPhone trade ins before iPhone 4, that they decided they would effectively cancel orders by denying the original price or waiting so long they say the offer expired.
They should have never approved the price in the first place if they didn't think that they would be able to pay. This company may make a quick buck now, but they won't be around for long....
Because of an isolated experience, then they "used" to be good?
Sounds like maybe you're just ticked because you tried to scam them and they caught you.