Although China was reported to have threathened to offer the J-11B/BS Chinese-developed Flanker copies for export not too long ago, more recent reports suggest the relationship between the two countries has improved and further military cooperation with China is envisaged. With China as a customer for the Su-35, the envisaged 300 aircraft might become reality. Rosoboronexport declared that it has offered China to sell an initial batch and then organize license production in China. Russia is also offering the Su-34 tactical bomber and Su-33 naval fighter. Apart from Russia, no other country is offering such advanced aircraft to China.
http://www.milavia.net/aircraft/su-35/su-35.htm
Las relaciones diplomaticas son algo arcanas, si es cierto que China no es un cliente fiel, por lo menos hasta ahora no es un cliente traidor que te hace competencia internacional con tu mismo producto, y eso que Rusia y China tienen una rivalidad militar natural por ser vecinos. China es simplemente un mercado muy grande como para ignorar, claro nada le gustaria a Rusia que fuera India quien le compre todo lo que no compra China pero este esta buscando la diversificacion. No es facil.