Boot Loop Data Recovery? Selling on eBay.

Selling my wifes boot looped 6P on eBay and I want to make sure the guy who does the "'un-doing" of the bootloop doesnt take all of her data and go on a spending spree.

From all the info I've read on how to "bring the phone back to life", is it wipes all the data off when you flash a new ROM.

Thought I'd check with all you smarty pants before I ship it off.

thanks.