Exactly: thieves don't care what you paid for it they care what they can sell it for and they can sell stolen Leica's for enough money that this is a real problem when buying stuff second hand. More so because whoever you buy it from may not know that once upon a time it was stolen. This applies to all goods that are resold but for cameras, laptops and smartphones it is a big issue because those are stolen with great regularity (and it is why manufacturers build in protection against theft in some of their devices and will not replace certain parts unless you can prove you are the owner of the device).
There is a whole industry in unbricking stolen laptops, for instance.