I honestly didn't consider the resale value of an iPhone, honestly. Wait, does Apple have a trade-in program or something of the sort?
Is reselling the device easy? I've never done anything like it, so I apologize for the questions if they're like obvious and what not.
yes and yes
Buy outright and resell - Privately; to a 3rd party reseller/recycler like Music Magpie in the UK (is this like swappa in the US?); trade in to Apple. Normally that goes in order highest price to lowest price, and reverse order of most hassle-least hassle. So pick your poison
You can also do payment plans from Apple but only on the 11/11 pro/pro max. Here again you have a couple of options
1) iUP - you sign up to a 24 months (US) 20 months (UK) 0% interest finance with Barclays. You pay either the tax upfront (US) or £69 (UK) as your first month. Then 23 months at 0% for the rest of the phone. After 11 payments (12 months) you can hand the phone back to apple, they'll wipe the rest of the loan and you can get another new phone - just restart the process.
This is convenient but a little expensive - you can also choose to sell the phone to get likely more money for it, settle the finance yourself and have a little left over. Then just do another iUP with Apple.
iUP comes with applecare+ to cover accidental damage, but that does mean you're paying $200 extra (spread over the finance period)
2) Iphone payments. Similar but lower cost option and less flexible. You're paying for just the phone (no applecare+) over 24 months 0%. No option to hand the phone back after 12 months. Naturally lower cost as you aren't paying for the Apple care on top.
You can still upgrade though - again just sell the phone yourself, settle the finance and start over with a new phone
Personally I'm doing iUP for the first time this year with an 11. If the 12 is a nice new design I'll sell my phone (more cost effective than handing back) and do another iUP with the 12.