Let's see what the SRD has to say on the matter
1. Players pay up, the GM compels for free
if a player wants to compel another character, it costs a fate point to propose the complication. The GM can always compel for free, and any player can propose a compel on his or her own character for free (ref).
What this means for you : if the GM compels an NPC, he indeed does it "for free", which means a Fate Point litterally springs into existence in his pool. This is still a compel. Something bad is happening to an NPC for that Fate Point.
2. This is not a cheat code
Whenever a scene starts, you get one fate point for every PC in that scene. You can use these points on behalf of any NPC you want, but you can get more in that scene if they take a compel, like PCs do.
You reset to your default total, one per PC, at the beginning of every scene.(ref)
What this means for you : With two limited exceptions, the GM cannot hoard Fate Points. Even by accepting compels and/or conceding, he cannot exceed that limit by much (I'm guessing conceding with a Main NPC fully loaded on consequences taken in that conflict could allow him to up it by four which, granted, may be much depending on party size).
3. Everyone has to agree on it
In order to compel an aspect, explain why the aspect is relevant, and then make an offer as to what the complication is.[...]
it should make instinctive sense, or require only a small amount of explanation, that a complication might arise from the aspect.[...]
The decision part should be very self-evident, and something a player might have been thinking about doing anyway. The same goes for players trying to compel NPCs or each other’s PCs—make sure you have a strong mutual understanding of what that NPC or other character might do before proposing the compel.(ref)
What this means for you : While the GM is the final arbiter, you can still argue that an action "doesn't feel like NPC X". As long as it doesn't happen every other compel, discussing the validity of a compel is to be expected at times and can be just as interesting a moment as any other part of the game.
If you still feel this is a potential source of abuse
As always, discuss it with your group. Maybe agree on a policy beforehand ("no more than 3 self-compels per conflict, please !") ? And if your GM eventually proves to be a repeat offender... well, that's another discussion entirely.