There's many ways thievery could be approached. If relations between shopkeepers are tarnished from picking pockets, it would be nice to have either a disguise kit or a (reliable) contact you can pay to retrieve items from a shop/NPC you're outlawed from. Drawback would be would have to wait for them to deliver the item after a short time, items may "happen" to cost extra on top of the service fee.
Add a feature for a delayed alert trigger timer out based on how much was taken or value of the item, the more taken/more valuable, the more time is hacked off from triggering the NPC's alert. NPC's will count you as suspicious if they found something missing and had seen you sneaking around or interacting with them very recently. Where as stealing something and taking a while for it to be found they'll be less suspicious of a theft unless the conditions become obvious, then they'll go into an alert.
Picking locks -
If a door is simply picked then it becomes obvious to the NPC that will contemplate whether it was broken into or they misremembered leaving it unlocked, if something is missing they will soon after deduce the lock-box/room/home/cupboard was broken into. results could be neighboring shops homes and NPC's raising caution of suspicious individuals, and they'll triggering condition: Neighborhood watch, guards in or around personal property. Finding unlocked locks will make them investigate for stolen items or other unlocked items.
Picking Pockets -
easiest to get caught, also easy for someone to alert something is missing depending on the item(gold, weapons, valuables). I don't like when NPC's have something stolen and they immediately happen to be looking for the item to find it's missing. Triggering condition: increase guard patrols on the streets and around shops with public perceptions to thieving increased. Difficulty can change based on whether the target is in crowded area, and distracted aside from other skills or racial abilities that might make them more perceptive to being mishandled. I like when picking pockets also show up in some dialogue options to demonstrate misdirection. Make it so pick pockets can fail to not take the item while also not always alerting the NPC
Stealing -
Depending on the value of the item, it might go unnoticed or quickly discovered. If you get caught, prepare to have to convince them your intention wasn't to steal, they'll either take the item back or report you, even attack you in some conditions (NPC that has no guards, or more evil)
Fall Guy - Maybe stealing in some aspects will certainly result in suspicion and interrogation of you, which could make it crucial to be able to have a fall guy, where if you can create the right conditions, clues can be left to blame shift to another NPC who will end up redeeming you of your sins, but not removing suspicions. If you get caught and all things increasingly stack against you, you'll be stuck with a ton of fines, jail time-- and considerably execution!
If certain common items expenses add up, then it can increase the value and appeal to resorting to theft, making it more tempting for the player, so that more upright individuals will not take risks or compromise their integrity if they really need to stick it through when they're low on gold or can't find much specific equipment that they may be able to steal from others. Like an economy, things often need to be balanced out to increase the impact of alternative options and make its systems effective.
Search skill could also be used to enhance findings of picking pockets, and to discover valuables in unusual places that would be previously less evident to the unkeen eye (items that can also be stolen creating more possibility to more bland/impoverished homes.)
Would also be great to see a minor trade simulating mechanic like with the option to smuggle in stuff which can expand horizons to all kinds of things depending on needs of people for quests, be it weapons, drugs, bodies, riches, slaves, shopkeepers illegall acquired goods, etc.
