If you have an used smartphone, and you want to just sell it there a some options. The first option, you bring your smartphone to mobile shop, and get an apposal.
But the new version from selling of used mobile phones are basically working online.
You have first to evaluate on the website your phones worth. After you get the shipment label for the package. After you send it to for example mobisto.de the staff check the technical conditions from the smartphone.
If the condition from the mobile phone is as stated on the evaluation, they wire the amount directly to your bank account also to your Paypal account.
If the condition is not as stated, then you get an email offer. If you accept these, the companies wire the amount too.
Here some companies:
Germany: mobisto.de mobisto rebuy.de cleveretronic.de