I can confirm, if you buy from Walmart and make no changes, the only difference is when restarting from a complete power off it will show the Walmart logo in the reboot. I've attached photos of mine showing power off, reboot and sleep screens.
There is no other indicator anywhere* that Walmart is involved.
That is all if you change nothing. If you go into the affiliate.conf file in the .kobo directory as mentioned, those traces will disappear. It isn't like Kindle where there are ads on the lock screen and ads on the home screen.
*If you do not choose "Show current read" in "settings/energy saving and privacy", then the sleep screen will show the Walmart logo. But really, who buys a Kobo and doesn't show the book cover as their sleep screen?
Edit: The Dragonlance covers kinda suck, and I dusted my Kobo after looking at the pictures I posted
