There is also the issue of ability.

Mechanical ability of the one installing it.

I don't know how many times I listened to someone bad mouth a product and they were the one that screwed it up.



The mechanical ability of the one writing the instructions.

We all know this one, right?



The ability of the one writing the instructions to communicate properly as there might be an assumption that the one installing the kit will make the same mechanical assumptions, and often they do not.

One expert explaining a process to another expert would leave out vital info a newbe would seriously need.



And the one sourcing the parts that will go into the kit might be nothing more than a purchasing agent or just a simple bean counter with no idea that a cheaper, or even a part that seems the same might not be the correct part!

I had this one bite me in the @ss on a regular basis all my life!

I am now paranoid when purchasing anything in a "KIT"