I have fared well by buying 1-year old used flagship phones in good condition.
Cost is a fragment of original price, battery is still fresh, and specs are great, being last year’s flagship.
Also, I tend to buy large-brand models, like Samsung. Not because I have a particular affinity but because it’s stupidly easy to get accessories for, say a Samsung Galaxy S10, as compared to a cheap Xihuawii Z2H or whatnot.