You get what you pay for I'm afraid, the ones I sell are top notch, or the other ones need work to make good, see thread below
http://www.350z-uk.com/topic/76138-nismo-style-rear-spats-to-clear/
If you really want to tart your rear end up there's this option:
http://www.350z-uk.com/topic/77291-rear-diffuser-and-spats-combo-230-delivered/