In various shows, movies, books, etc, thieves often intend to steal from wizards or, if they're lucky, from a treasure horde of long dead royalty or such and, almost as often, either set off magical traps or pick up some ancient artifact that has some adverse effect on them or entire lands. I would think they'd be more cautious, especially when there's, e.g., a purpose built cradle for an unreasonably large gem. (At its most common, picture the gem Abu picks up in Aladdin.)
In worlds where magic is a well known, common mechanic and often feared, would it be reasonable for thieves, at least high end ones, to show better judgement about these things, possibly to the point of studying common tells, if not much more intimate knowledge about their intended bounty (if it's known)? At this point, I'm assuming a professional thief, not just someone who's down, out, and dabbling in a life of crime.
Edit for Clarification:
- Assume D&D style magic: enchantments, traps, direct magic, etc. Almost anything goes, if the wizard is powerful enough. Traps are simple enough for almost any home owning wizard, so I'd imagine they'd be common. Materials are used in casting, but assume the cost is negligible if an item is worth protecting. An undetected trap could disable, maim, or kill an intruder.