Every ebay and/or Amazon Marketplace vendor is an individual seller - neither Amazon or ebay have any input into the source of the product or the quality - if you were to ask your question referring to a specific product or vendor, someone who has purchased that product from that vendor might be able to share their experiences, but, asking the question the way you did is akin to asking "how long is a piece of string"?
I'm sure some of the kits are excellent quality, and equally sure that some are junk.
98 - 1.8 Mitsubishi Pajero iO
98 - 2.0 Suzuki Grand Vitara - SQ420
05 - 2.0 Suzuki Grand Vitara - JB420
15 - 2.4 Kia Sportage