I think that GM intervention in the case of thefts is too OOC. The only way to prevent OOC thefts is to make it really hard to happen. IRL if you get your stuff stolen, you have the possibility of claiming it back if you see the person or people who did it. You can show up with an AK-47 and get your things back or die trying. Something like that should be available but not through OOC.
When a player gives an item or puts it on the ground for RP purposes they are pretty much aware of the item itself: they are "using" it somehow. So it is unrealistic that anyone could just walk by and take it and walk away freely, that's OOC. If they do so, they should be noticed by the owner and the owner should be able to react accordingly. Then maybe a "/watch item" command could be created. It would work something like this:
- When a player takes an item out of their inventory they could right-click on it and activate the /watch item command (before dropping it, if the item isn't dropped within 10 seconds, the command is cancelled). So they don't lose sight of it. The command will be active until the item is placed back into the player's inventory. A player can only watch a limited number of items (one? two? three?).
- Items that are "watched" can be placed on the floor. If another person attempts to steal the item, a window pops up before the item is picked up (yet after the /pickup command has been used). The thief would see a message like this: "You are attempting to pick an item that is being watched and that belongs to someone else. Do you want to steal this item? If you accept you will be challenging <Name of the watcher>" By clicking "No" the item will stay there and it would be as if nothing ever happened. By clicking "Yes", the person watching the item will receive a message like this: "<Name of the thief> is trying to steal from you and has challenged you to a duel. Will you attack the thief?". By clicking "No", the watcher declines the duel and allows the thief to take it. By cliking "Yes" they will fight. The winner loots the item in question from a "Quest Reward" sort of window. This way a very intimidating thief can come along and just take the item, while the guard is unable to stop them, RPing he is intimidated by him or maybe they will argue and fight but the crime will not go unnoticed and will have consequences IC. An automated shout could be added to the action too: by accepting the duel the owner could /shout "Thief!" or a personalized message of the sort.
- When an item is placed on the floor to be watched, more guards can join in. By using the watch command on the item, they would get a "Do you wish to help <Name> watch this item?" message. By clicking yes, they will receive the same message as the owner if any thief dares take the item. Thus, stronger protection can be offered.
- Lending an item to other players is always a risk, just like IRL, and that shouldn't change much. When you lend something to someone else you never know what may happen. They may not wish to steal it but sometimes they just get robbed themselves and then: bye-bye Rolex. If they betray your trust, RP around that. And if you don't know a player that well, Nikodemus' suggestion of a special trade window for /repair should be available. If you just want to show someone your newly acquired sword you can drop and watch the item so the other player can check its stats or use the regular /trade window without clicking "accept". How you decide to do it would be up to you, but each bares a consequence. If you trust they will return the item, it's at your own risk.
This way, robberies would remain mostly IC (you see the oportunity and you willingly commit the crime), and stealing something OOC would only be possible using characteers that trust each other enough to use the "full" /trade window for medium to long term loans, and considering that most players won't steal form characters they consider friends, OOC theft risk would be greatly reduced (probably to the cases like the one I mentioned earlier about someone from dwarvesbane getting mugged, which should be addressed by GMs since it would be totally OOC and mean spirited from its conception).