Apple's trade-in policy is rather good!
I rather fancied a new Series 4 watch, ordered one for pick-up and went to my local Apple store to collect. I happened to be wearing my Series 3 watch (bought when they first came out) which was spotted by the customer service guy who asked if I would like to trade it in? OK I said how much? He looked at the watch, removed the strap and said £150. Deal I said!
He knew from our conversation that I have umpteen Apple products and asked if I would consider other trade-ins? I have 3 iMacs and would maybe consider one of them. I need them because they are all at different software levels to support legacy apps. I have a similar problem with iPads, again because many legacy apps are no longer supported under the latest levels of IOS.
Going to have to give this some serious thought.