For several decades it's been common for weapons sales to be accompanied by restrictions on how those weapons could be used. These usually include prohibitions against using the weapons to attack a neighbor, or sometimes even against a faction in a civil war. The restrictions are the result of local politics. Arms sales are a contentious issue. While politicians want the jobs, there is also the moral issue of how the exported weapons will be used. For thousands of years, selling, or giving, weapons was a quasi-religious action and was not done lightly. But selling weapons without strings has become marketing advantage. Secretive gunrunners have always had a "no strings" advantage. 

But high tech weapons are another matter. The restrictions work particularly well for high tech weapons, which require frequent support from the manufacturer (spare parts and technical assistance.) In cases like this, you are at the mercy of the manufacturer to keep your complex weapons operating. An example is Indonesia, which got into trouble with the United States and Britain (which supply most of Indonesia's military aircraft). Over the last few decades, Indonesia engaged in some pretty brutal behavior trying to suppress a separatist movement in East Timor. Now the U.S. and Britain are withholding spare parts and technical support until Indonesia prosecutes all the officers and soldiers who took part in the East Timor atrocities. Indonesia can't go after the accused troops quickly because many Indonesians approved of the brutal tactics. But as a result, some 60 percent of their air force planes are inoperable because spare parts and technical assistance is not available. As is increasingly common in such situations, a less sensitive supplier is sought, and that usually turns out to be Russia or China. Russia is now the leading supplier of inexpensive, high performance warplanes, and a novel deal was made with Indonesia. Only 13.5 percent of the price was paid in cash, the rest was in goods (palm oil, cigarettes, electronic parts, rubber and so on). The Russians are in the process of delivering two Su-27s, two Su-30s (both roughly equivalent to the U.S. F-18) and two Mi-35 gunship helicopters. Two dozen Indonesian pilots and mechanics are in Russia being trained, and 30 Russian technicians are in Indonesian taking care of the arriving aircraft. And this deal was really creative, as the Indonesian government knew it could not get the money out of the legislature for these new aircraft. So the deal was made with the National Food Agency, which supplied the cash, and other government agencies scrounged up the goods required to fulfill the rest of the payment price.