The Rambam writes (Hil Gezeilah ch 1) that the issur of lo tachmod is violated if a person covets his neighbors property and talks him into selling it. Ra’avad disagrees and writes that so long as the neighbor says “Rotzeh ani” – “I want to sell it,” there is no prohibition. According to the Ra’avad, lo tachmod is violated only if the coveted property is seized a against one's neighbor's will.
Rambam writes further that there are no malkos for violating lo tachmod because it is a lav she’ain bo ma’aseh. Ra’avad disagrees and opines that the reason for the lack of malkos is because lo tachmod is nitan l’tashlumin, the object taken must be returned.
The Magid Mishne suggests that these are not two separate issues, but one point is contingent upon the other, l’shitasam. The Rambam holds that lo tachmod is violated even if a valid sale is done and there is no obligation of tashlumin; the reason for the lack of malkos must be because there is no ma’aseh involved in violating the lav. The Ra’avad who understands lo tachmod to be seizure by force, an active ma'aseh, is forced to invoke the idea of nitan l’tashlumin for the dispensation from malkos.
But why according to the Rambam are we so convinced that this lav lacks a ma’aseh? True, talking a neighbor into selling something does not involve physical action, but coercive tactics are not limited to verbal pressure alone. One can easily imagine a scenario where all kinds of action are involved in pressuring someone into a sale.
The Steipler (Birchas Peretz, P' Yisro) answers that the issur of lo tachmod is not the effort to obtain a neighbor’s property – the issur is coveting a neighbor’s property, the emotion and desire. However, that desire must make itself manifest before halacha recognizes it. Lo tachmod is defined as a lav she’ain bo ma’aseh because the deed or talk involved in obtaining what belongs to someone else is just an indicator of the desire of the heart, but it is that desire which is the actual subject of the issur.
Another example of the same idea: Tosfos (Shavuos 4a) writes that if someone took an oath to eat a specific loaf of bread and then threw that loaf into the sea, he would not get malkos because the violation of the shevu’a, not eating the bread, is a lav she’ain bo ma’aseh. Question: in this case the person did a ma’aseh by tossing the loaf into the sea, so why is there no malkos? The answer again is that tossing the bread in the sea is just a demonstration that the person does not want to eat it, but it is the lack of eating which is the actual violation of the lav.