I am in the process of purchasing a used Android device through eBay. Assume I receive it, it is exactly the model I expect, it appears to work, it is not encrypted, and it is not stolen, etc.

I am planning to do a factory reset on it when I receive it. Is there anything else I should do to ensure that it is not rooted and that no malware etc. is present? I don't know enough enough about rooting to know for certain that a factory reset will eliminate that.

If I were selling one, I know I should encrypt, perform a factory reset, and possibly load with data and perform another factory reset.

Thanks,

TRRed

That's about right. You could also check the ESN too, Swappa has a tool for it I believe. You can also get Android erasing tools. Or once the phone is wiped, load videos on it, factory reset again. Once done you can see if it has been rooted by installing a root checker tool from the play store. You could also put Avast on as that is OK.

Generally speaking, that's the advice given when selling & buying pre-owned Android. But, it's been known that the "internal" SD card (partition setup for data) aren't necessary fully wiped & clean of stored data, hidden folders & files can still be there and/or recovered, with the proper tools (apps). See this recent article here - http://bgr.com/2015/05/22/android-fa...et-erase-data/

If the device was rooted, a factory reset is not sufficient to unroot it - there are specific procedures, varied by OEM, to do it & it can "brick" the device. Yes, you can download free apps from Google Play Store to check your device status on whether it's been rooted. If it's been "unlocked" - during bootup, a warning message will pop-up to alert you - devices running "older" Android OS don't always do that - and, it can be "patched" to hide the pop up.

Depending on your level of skills & familiarity with Android SDK tools or OEM factory tools (if available, i.e. Motorola, HTC, Nexus, etc.) - you can download and flash a clean factory image, cleaning everything. If you can access the recovery or bootloader menu, there are usually options to wipe - if you aren't comfortable or afraid to soft or hard brick the device, get a geek friend or IT buddies to do it for you ... a process that generally take 10 to 20 minutes, as the procedures & flags for caution varied with the device.

** Before doing all these, you also want to check to see if the device (using a Sim card) is unlocked (for any GSM carrier) or locked to its carrier only (AT&T, T-Mobile, etc.) by putting in a known Sim that's working - contact the seller if there's any question.

Once done and you have it setup, install a trusting free App like "Mobile Security & Anti-Virus" by Avast, to scan your installation & settings. Sites like Android Central and XDA-Developers have device-specific info, FAQ, troubleshooting & tips on how-to, etc. if you feel confident to give it a go.

Carrier-branded & OEM often install "extra" apps on the device, referred to as "bloatware" - some are useful while others (most) are not - in enhancing functionality - you can sometimes disabled or block it, but usually cannot uninstall or remove it, especially with unrooted "stock" rom on the device.

Thanks to both of you.

TRRed

It'd be easier if you mention which device exactly.

First off, start by doing a factory reset.
Then boot into stock recovery.
Wipe data/factory reset (3 times)
Wipe cache partition (3 times)
Reboot

Or you could repeat the steps above, flash the latest stock firmware and then wipe internal storage again.

If it's a Nexus, great way to do it is by re-flashing the userdata partition and then doing a clean wipe through recovery.

Device is an Asus (Google) Nexus 7 2013 (LTE).

Thanks.

Now, id' the device made it much easier.

Link for XDA - it has 10X the info you ever needed to know, running MM 6.0.x now, factory stock - most likely, previous owner restored to full stock, relocked the bootloader after unrooting, that's what these devices are for.
http://forum.xda-developers.com/nexus-7-2013

I have a 1st. generation Nexus 7 (2012) and travel with it, manually upgraded to MM 6.0.1 with a custom rom. You do NOT have to any of that - odds are good that the seller restored it to stock condition before putting it on eBay.

Look to see if it has a custom recovery - TWRP typically used or stock by Google. With TWRP, you can flash a stock image in *.zip format easily with a full wipe, etc. - read those steps & follow instructions closely - grab a cup of coffee while PC is installing drivers & software, before rushing off to do it. Otherwise, with factory recovery - you will need to flash the ROM image differently - best way is to use Android SDK tool. Otherwise, Nexus Root Toolkit in XDA forum is the easiest way to flash. This is a weekend project, not a rush one - to avoid turning it into a paperweight, spend the morning reading & reflash the image in the afternoon, reboot & setup - by evening, you will have a good-as-new N7 in your hands.

There is quite a bit to learn & get familiar with, which I won't go into here on a travel subforum. Google has a dedicated N7 forum for users to share & get help, along with XDA. Turn on Developer's Option & enable Android debugging mode - to allow full access to internal SD drive, and to check that Android Device Manager is installed & configured to work, that will give you a great deal of control with permission settings while using it, or in standby mode. Have fun