I'm always dubious about buying a phone locked to ee as it's unlikely the person who sold it to CEX bought it outright, which means that it is still property of ee until it is 6 months old (as per the contract terms and conditions) So unless cex are ok with refunding it if anything goes wrong...
I wouldn't see why not, just say you'd rate it at grade C, and you're really disappointed
Do you think they'd accept the return if you weren't happy with the condition without any argument?
For £525 yes, the popular colours are more 😔
Is it just this colour?