Erasing data on old smartphones prior to sale

[46and2]

Hi All

My phone bricked itself at the start of the week and I got a new one (old one was a samsung galaxy s6), I had to do a full factory reset on the s6 and have since managed to revive the phone and get it working reliably. The phone was up to date before it bricked.

Does anyone have any easy/uncomplicated ways to ensure all my data is erased before I sell the S6 on ebay/other? I have read that the directories may be erased but the underlying data is still present.

Just looking for suggestions from people with experience

Thanks

[e-honda]

S6 launched with android 5 which did not have encryption enabled by default, this setting would most likely have persisted through the upgrade to android 6 and possibly 7, so unless you specifically enabled it or did a factory reset there is a reasonable chance there was unecrypted data on your phone.
Factory reset will have overwritten some of your data, and made the rest of it more difficult to recover but far from impossible.
Quick and easy way to wipe the empty space is to download a large file, say 1gig+ then copy it repeatedly till you run out of disk space.
It's possible that small pockets of previously unencrypted data might avoid being overwritten and still reasonably accessible but the risk of this is low.

[46and2]

Great reply thanks