The PC's are hired to retrieve a family heirloom which was stolen from the family 5 years ago. The family has just found who now has the heirloom and want the PC's to steal it back. The current owner is the original thief and is an accepted member of the community. The theft must be done quietly so as not to attract attention as the familiy would lose social esteem if it was known that the object had been lost i.e. no questions asked in town etc. The current owner has a normal house with normal traps and precautions to protect this type of treasure, plus whatever skills or guards are required.
After the theft has been performed, the object handed over and the PC's are still congratulating themselves on a job well done, reward posters go up around town for the return of the object, the thieves wanted dead or alive or the object returned and no questions asked. The PC's have been suckered, the object has ALWAYS belonged to the person they stole it from and they are forced to either flee the area (never to return), or to get it back again from the person they originally stole it for (probably a member of the local Thieves' Guild or similiar). The preferred method is to lead them toward stealing it back again (if they can break into the thieves' guild etc) as there are no other safe alternatives. If they are captured, no-one will believe them unless the PC's pay for a cleric to "Detect Lie" (very expensive under the circumstances) and no-one will mind if they are accidently killed while trying to retrieve the object.
Last time I did this the object was a diamond tiara and used in royal coronations (one of which was due in 2 months). Nearly brought the whole political structure down.