One very simple set of rules could be: 1. your app may not accept in-app purchases more than once per month, and 2. the in-app purchase cost must not exceed 10% of the original purchase price. And then 3., there should be a lifetime maximum on purchases, i.e. you can finally “pay enough”. Instead of these or really any other sane constraints, we’ve somehow made it worse by now preferring subscriptions !!! And even mo…
i'd go with a monthly limit. one that doesn't break the bank, but one that also isn't to low to make it not worth it for the game developer.
how about $10 per day and $50 per month?
then you can spend your weekends playing away and buying to your hearts content. and if you instead do that every day, well then, you are going to have to ask yourself: home come that at the end of the money, there is so much month left over?
another measure would be the cost of a pack of cigarettes. at what point does smoking affect you financially? i think there may be studies for that. that same number ought to apply to games.
now there is still the problem of multiple games. so maybe another cap for overall spending. but that is trickier. how does that cap distinguish game spending vs using an app to buy groceries online?