I have been on both sides of the coin. I actually had a sellers agent teach a seller how to play a slight of hand trick. Stained carpet? No problem - put an area rug on top of it.
As a buyer I want full disclosure - in the absence thereof, I will not hesitate to poke and prod myself. As a buyers agent I will do the same - poke under that area rug; prod under the sink. Look at the exterior as if it were my front living area.
Leave no stone unturned - and if slight of hand is afoot - walk away.
As a buyer's agent I do my best to ensure my client and I do the best due diligence before the sale so as not to experience remorse later.
So the answer is: Due Diligence