As a general rule, most TSA agents have enough integrity and scrutiny that they won't steal anything from luggage. They are watched pretty closely by people who can't really afford to lose their job, and there are better procedures in place to file a claim against the agency if your luggage has an approved TSA lock on it, you have a bill of lading (packing slip, inventory of contents), even just pictures of what was in there before the trip. When they find out that only TSA agents were allowed into the luggage, the excrement will hit the fan at the office. It'd be like someone opening your fed ex package at the processing terminal. It just doesn't happen often enough to worry about.

If you check baggage, use luggage with approved TSA locks. If I can make it in and out of Baghdad to Seattle and all points in between without losing my knives, lighters, cameras, money, etc. then it should be good enough for just about anything else you might pack.