The scenario you're describing is exactly what we try to prevent with our code review option. Likewise, every app we broker is listed publicly on either the AppStore or Google Play, so every buyer can and SHOULD download the app to preview it.
I should also note (which I hoped was obvious, but after re-reading the post and thread I realize it isn't), that we actively reached out to this buyer to see what was wrong and what happened. We even gave him the opportunity to withdraw the chargeback and indicated that we would continue to do business with him. Even though it's somewhat of a moot point, this chargeback was not the result the buyer being misunderstanding what he was getting.