I've noticed a lot of games in the Mac App Store are starting to have a single "unlock full game" IAP. These I really like. The good ones have enough content to show the nature of the game, get me hooked on the mechanics or story and lead directly into the single unlock.
It's a classic shareware model and results in my willingness to pay more for games because there's much less risk. The good ones also are very explicit in the description on the App Store that it is a first level/trial with IAP.
Like old school shareware, where you got the first episode to play through and then could purchase the rest of the game for a small fee.
As for the guy's situation it sounds like they need some more nag screens and easier ways of sending them money. (Well it is currently a lot easier than the old days of shareware, no envelopes to fill out, just a button to press.