The Rambam says that one is only עובר on לא תחמוד if he nudges his friend to sell him an object and then he actually buys it. But if he doesn't acquire the item he wanted, there is no לא תחמוד [we won't give him the "best middos" award in camp but that is a different story...]. There HAS to be a מעשה. Then he says that there are no מלקות because it is a לאו שאין בו מעשה.
If the Rambam weren't about the brightest person in the last thousand years I would think something is wrong. He says that one is only עובר with a מעשה and in the same breath that it is a לאו שאין בו מעשה.
The interlocutor of the Rambam, the Ra'avad, never one to mince words, lays it on heavy. "לא ראיתי דבר תמה גדול מזה".
