I've only been running ACKS for a few game sessions, by my players managed to loot a few thousand GP and are thinking of what sorts of things they can afford to buy now. They are especially interested in healing items, because they have just one Priestess among their fairly large team (they're using lots of henchmen). I told them that buying a potion of Cure Light Wounds was 1,000 GP, but buying a once per day "wand" of CLW would only cost 10,000 GP. Since they're sure to get more uses out of it, from my perspective it seems like it would be foolish to buy potions instead.
I note that by sellign the casting for the default market price, the 1/day CLW pays for itself in 33 months (10 kGP/(10 GP*30 day/month)), so that seems in line with the ROI assumptions built into the rules for someone to have one commissioned. A spell caster who had created one previously could start crafting them for only 2.5 kGP though, right (with some chances to fail)? Even in a relatively modest community, it shouldn't be too difficult to get a handful of these spells being sold each day, giving the crafter a considerable ROI. I have read mention of the Fragments of the Tablet of Destiny being used to limit or prevent creation of disruptive or unbalanced items, but it seems like a 1/day first level spell item shouldn't be in that category quite yet, even though it already feels problematic.
Now, imagine if some enterprising divine-type crafted a 25,000 GP unlimited item of CLW, instead. They could move to a class I market, capture virtually all demand by selling CLW for only 2 GP instead of the market rate of 10, and net on average 900 GP per day (even without increased demand which would presumably follow reduced cost), which paid for their item in just 1 month. Compared to the 150 kGP Ring of Regeneration, the unlimited CLW item is even better in some ways (multiple targets, can use after being injured instead of locking it to one person), despite being much less expensive. This feel firmly in the realm of too good to be true.
My question is: should the Permanent Effect items for healing even be creatable? If so, should they have an upper limit on frequency? Should I raise the price such that they take ~33 months to pay for themselves? If healing items are problematic, does the same apply to every spell that has a reasonably high market demand? What about spells that are implausible to sell (or sell at scale), such as Magic Missile?
I understand that someone who tried to disrupt the spell market on a large scale would be the target of numerous hijinks, but assuming that they're in cahoots with the local leader of the biggest thieves guild and the king, and this kind of thing could go on for a while before someone manages to put a stop to it (and they might steal and perpetuate the problem). I'm not especially interested in ways to deal with a problematic item, but with which items should and shold not be allowed.