The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at the Trope Launch Pad.
A downplayed variant of Fake Wizardry - you do have some powers, they're just not anywhere near as good as the ones you're pretending to have.
The Myth Adventures jump to mind here; the protagonist is either a terrible wizard or a really, really good one depending on how you look at the mileage he gets out of his spells- all three and a half of them. Later on as he improves, he gets an apprentice who wants to learn to be a proper mage after doing something similar with a massive collection of Magical Jewelry.
Edited by Scorpion451

The use of a magical power (technology, special effect, etc.) is faked by combining other ones.
For example, in a setting where magic exists but bringing people back from the dead is truly impossible, a scammer claiming to resurrect people actually uses a combination of telekinesis (to move the body), ventriloquism and mindreading (so the dead person can tell relatives what they want to hear).