How do you ensure you’re not scammed on those sites? Apple’s trade-in values are too cheap.
Sell it for cash locally. Bring a UV flashlight to check the money. Sell in front of a police station or in a public place. It's not perfect. But there have been plenty of complaints here about Apple's trade in partner. That I don't see it as any more of a sure thing. The only sure bet price wise with Apple is if you trade in at the store.
As for eBay I wouldn't risk it on any highly sought after electronics over $100 as a seller unless I was a power seller. It's too easy for buyers to scam you. Other items are fine or electronics which aren't highly sought after. Like I wouldn't expect there are too many scam buyers for a vintage Commodore PET as for a three year old Macbook or year old iPhone. They want something they can easily flip.
Still by and large there aren't many scammers on eBay. It's probably overblown. I'd just hate to lose $1,000 laptop that way.