I’ve tried selling my iPhone through various platforms:

Online Platforms:
You need time to answer questions, share photos, meet buyers, and may deal with lowball offers. It works if you have the time and patience.

Third-Party Retailers (e.g., SenQ, Machines):
Straightforward and convenient, they inspect the phone on the spot, I think now online is possible too. It’s quick, but the trade-in value may be lower than selling it yourself.

Apple Store:
Best experience so far. Just walk in with your phone, they scan, inspect, and give you an offer within minutes. I found the fairly price, and the whole process was quick and hassle-free. You’ll receive store credit in the card that to use for your next purchase.

Overall, I’ll stick with the Apple Store going forward, it’s just too convenient.