white smoke and a rough idle

[farm stroker]

So im looking into buying another truck, but it has some issues. Im going to post the link on craigslist to it, my question is with the repairs and checks he's done on the truck does anyone have any thoughts as to what else is wrong? (i havent talked to him yet, so idk if he has receipts or anything to prove hes even done what he says he has)

2001 Ford Powerstroke Mechanics Special