Most after market cheap bodykits are complete and utter crap. They don't fit properly, aren't made with any structural strength, crack, and cost a fortune to fit properly.
Note the word 'properly', i have seen loads of kits fitted to various makes of cars and the owners have thought they were excellent, a closer look at them with what is perhaps a critical eye says they are garbage.
Maybe i'm just too fussy !
I always wanted a Pitroad M kit for my GTO until the first one arrived at the workshop for us to fit for a customer. To make £1800 worth of bodykit fit 'properly' and look good, cost the customer over £1K. Side sills had to be cut and reprofiled before they would actually attach to the car in more than two points. The nose cone just didn't fit at all and had to be cut etc, as with the rear cone.
A carbon bonnet, of which there are many manufacturers, was just appaling, the finish was very poor, the fitment even worse. We had to grind out the inner skin so it would shut and clear the strut housings.
The customer was fully aware of all this and was told so and shown prior to work commencing and given a photographical journal of the work progress.
I'm sure there are some good after market kits, somewhere, but the ones made for the car by the manufacturers or for the manufacturers will always knock the spots off the cheap bits of junk that haunt places like e-bay.
A cheap body kit can soon become an expensive one if it needs 30 hours of labour to make it fit your car.
My advise is to do lots of research, also ask a few known quality bodyshops about what kit will fit with minimum hassle or not too much altering.
Be aware of cheap quotes from companies just to get the work through the door. It doesn't always mean the job will be bad but most of the time you get what you pay for in life.
Have a look at any other work currently in progress too if the chance is there.