The semi-legal buying and selling of arms, technology, and equipment is centered in a few places on the planet where the local laws can be worked within. Both Switzerland and Port Placido are high on the list of the most frequented countries for this type of transaction.
A grey market item is one that is legal to possess or use in one olace, and illegal in another. This is opposed to black market where the item is illegal in both the place of origen and the destination (and just about everywhere else). An example of grey market product would be personal military grade weapons, which a number of countries severely restrict, if not outlaw, ownership of. Other countries, such as texas, have no laws concerning personal weaponry, so the end result is that the legality of such weapons depends entirely on which side of which border you are standing on. The grey market exploits this.
Certain countries on the grey market depend on a percentage of the sales for their GNP, and provide protection and support for grey market activities conducted within their borders. Chief among these are Port Placido, Palestine, and Hong Kong.