If my roll falls short, I either have to spend some Fate points (which I completely understood from the example), or take the added mental stress (ouch), or let the backlash go as it may, which is determined by the DM. If I AM the DM and this is an NPC, then I should pretty much be a good DM and let that help the players.

Other posters have well covered the mechanics, but I wanted to comment on this. Fallout is by definition a bad thing. If your players can get their disadvantageous circumstances to work for them, that's good, but your job isn't to make fallout helpful, it's to make it interesting.

What kind of a fight can your PCs put up? Refresh isn't a very useful metric; it's possible to make 20-refresh characters who would get splattered by two gangbangers with AKs, and it's possible to make 8-refresh characters who can easily manhandle an armored column. If you have a WCV who can pump out a ridiculous amount of AoE shifts of Incite Emotion, and the opposition doesn't have a counter for that, it can very well shut down mortal soldiers however well-armed they happen to be. If one PC has Superb Resources and Windfall, and the merc leader has the aspect Anything For A Buck, it's going to be a real short negotiation.

Generally, magic replaces skills rather than adding to them. So 4 shifts for effect would let you roll an effective Empathy 4, for the duration (in this case, 2 shifts sounds like about a short scene's worth of interaction). More shifts would let you have an effectively higher Empathy, or have it for a longer duration. If the spell is weak enough, or your natural Empathy is high enough, it might not even be worth using.

You do know you just described Bob, right?

Good point; since he's not really supposed to have him, Harry can't really go to the Council for help with the matter (also he's kinda on bad terms with them in general for various other reasons). So there's one major hurdle cleared for prospective thieves.

The only thing you'd have to worry about, then, is making an enemy of a powerful and dangerous wizard and his allies. No big deal, right?

Incidentally, while 'blampire' is a great word, I always call them 'blackulas'.

It's also probably a pretty rare thing. If the other wizard is less powerful than you, you can probably get nicer stuff on your own without stooping to petty theft. If the other wizard is more powerful than you, it's borderline suicidal to give them a direct sympathetic line to you by having their stuff. In terms of magical stuff, most of it is specialized or personally attuned in some way and won't be as useful to anyone other than the wizard who owns it. Essentially, it's absolutely not worth the trouble for wizards to commit acts of petty theft against one another.

For acts of grand theft, when it's worth the while of high-level wizards to cast divinations into the matter, it's nearly impossible to get away with it anyway.

The only time it's ever gonna happen is if one wizard has something that's

a) useful or valuable to anyone else

b) that is sufficiently unique or difficult to obtain that another wizard would rather deal with an incredibly dangerous individual - with access to magical divinations and traps - than pursue any other avenue of procurement

c) the wizard in question cannot or will not simply bargain or negotiate a trade, purchase, or borrowing of the item

d) the thief is confident that scrutiny from high-ranking members of the Council - people with centuries of experience and broad and powerful abilities to gather information - won't put him squarely in the Wardens' crosshairs.

That's a lot of ifs. All it takes is one victim running to the Merlin and getting your theft scryed to, at best, give you a reputation as a liar and thief before an audience of immortal peers with every reason to hold grudges, or at worst getting you in hot water with a law enforcement organization known for favoring capital punishment.

Stealing from other kinds of supernaturals has most of the same problems.

What you want to do is blind a guy, long-term if not permanently. Use a ritual that does this.

It hardly matters whether you do this by damaging his eyes, his brain, his soul, by cursing him with terrible visions whenever he opens his eyes, by hypnotically convincing him that he can't see, by sympathetically blindfolding a voodoo doll, or by creating portals in front of his retinas that send light to another dimension.

Use sympathetic magic to make you magically sensitive to physical phenomena.

Use Air magic to carry vibrations and smells in the air to you from a distance.

Use Spirit magic to enhance the light in the area.

Use Earth magic to sense vibrations in the ground.