It was nearly 16 years ago that I was first introduced to the idea of “the idiot check”: a last minute, top-to-tail, make-no-assumptions check before you turn out the lights and close the door behind you. It’s served me well on countless Web projects over the years, and it’s good to be reminded of it now and again.
On a weekend away with a group of my Uni friends, Dana, a lovely girl of Hungarian stock with a practical streak a mile wide, insisted on performing one last check throughout the entire holiday house before we could lock up and leave. Instructions were simple: look everywhere; don’t check your own room; check everything. She called it ‘the idiot check’: the check you do so you don’t look like an idiot.
On that occasion we found: a pair of ear-rings in a bedroom drawer; someone’s toiletry bag in the bathroom (we all must have been through that bathroom when we were packing up, but there it was); and EVERYTHING still in the fridge (it was so obvious to everyone that the fridge needed to be emptied that we all assumed someone else must have taken care of it already).
In a sense, this is what a lot of usability testing is all about: test everything – even the stuff you think is obvious – just to be certain. And it’s also what a good project manager or Q&A person or friend will do at the end just prior to launch. We know that over the course of many days, weeks or months we’ve gotten so close to the project that we’re no longer seeing the forest, and yet we also hate that person who comes in right at the end of a project and points out a bunch of things that could (quite clearly) be improved.
A fresh pair of eyes is a wonderful thing. A pair of eyes free of assumptions; with no baggage or knowledge of all the little decisions that were made along the way. Someone who doesn’t think it’s too stupid to look in the fridge for your sunglasses that simply aren’t anywhere you’ve looked since, by definition, they’re somewhere you haven’t looked and that includes the fridge, right?
The Idiot Check requires that you set aside your pride and be prepared to look silly. Just remember that it’s better to look silly on your own terms with people you know, than publicly and by accident 
Great practical example — so much of the value in ux consulting is doing just this. Steve Krug calls it advanced common sense, and it is as you suggest: a fresh pair of eyes with a different perspective on the rental. Of course, it’s oversimplified, because on the Web you’re also checking to see if the rooms, and the path between the rooms makes sense to the people who are “renting” it along their path towards a goal. But it’s funny working with design teams who have already checked that bathroom “a million times,” much of the work is letting them know they left the place a mess without them feeling like all their work wasn’t really cleaning, but more of a light dusting — without it bruising their ego too badly