Even the used-2nd hand market, when it comes to Apple products, they hold their value much better then any phone, computer brand in the market, from what I have seen in the past few years.
From what I have seen today at Best Buy. An iPhone 7 and iPhone 7 Plus, still sells for full retail price when it came out on day one.
Like new iPhone 7plus 128gb, sells for $550 on Craigslist.
If you wait 3-4 years, then you’ll get a better deal. But not today or in the next few month.
Good luck.