Chinese have sold third class military hardware to Pakistan, Bangladesh and many other countries…… Here is the description of defects in Chinese built and sold Pakistani Navy frigates and their much spoken of JF_17 fighter jets and many other items;
The Pakistan Navy is facing problems with at least four of its Chinese-made multi-role frigates, according to a recent analysis by Geopolitica. Earlier, there were reports that Pakistan was facing issues with naval warships and even with JF-17 fighters that Islamabad acquired from China...
eurasiantimes.com
Any country who buys it once from China other than political reasons, never returns. Pakistan has no choice because nobody else will sell to them. The danger is that their technology will be passed on to the Chinese.