100% go new, at least since battery replacements stopped being trivial.
Love this phone it's what I'm using now but wouldn't pay this for it even if it was new. Paid £235 for mine new from Amazon 18 months ago. So based on that it holds its value better than iPhones!
Probably a chance I'd take to save £30 on a used/Refurbished Smartphone Or spend 25 more for brand new sealed if you really wanted one.
"A fully functioning device with light but visible marks on the screen and body." Seems like it would be between a grade b and c to me. Only used them once but the grading was accurate on my "pristine" op8 pro
£25 more for new at Smartfonestore, or £30 less for grade good Smartfonestore https://www.smartfonestore.com/search/Mi%209t