Genuine vs aftermarket parts

“Genuine” parts are inevitably more costly than aftermarket ones, even if they appear to be identical. Legal liability is the absolute fundamental issue underscoring parts selection. In the event of a component failure, the results may vary from minor annoyance to life threatening peril.
Trivial versus non-trivial components
Only a professional workshop has the knowledge and experience to decide which components meet this fundamental criterion. They will also know when an after-market part is actually better than the original and is non-critical for safety and operational reasons. In some cases, the after-market part may be better designed and more robust than the OEM version. After all, technology improves and difficult-to-fit parts may be redesigned for easier installation Therefore, the legal liability aspects may not apply to some components, but it is the experience of the specialist that is critical. Sourcing your own parts then expecting the workshop to fit them is absurd. No professional shop is going to take the risk
It is also worth considering that every vehicle is built to a price and market niche. The engineers and accountants will inevitably have different views not only on the level of inclusions, but also on the cost of each and every component. The original equipment manufacturer (OEM) may source parts for virtually anywhere but they have the responsibility of testing, ensuring compatibility with other vehicle components and above all, the effect on vehicle warranty.
Some examples
For critical systems, engine, drive train and brakes are just some of the vehicle components where OEM parts are essential, not the least for the warranty and legal liability issues described above. It does not matter where the OEM sourced the part, it complies with manufacturer specifications and warranty.
Conversely, suppliers like Maxidrive, Bilstein, Hella, IPF, Haltech and others provide components that are tried and tested, with years of satisfactory service. Their products often out-perform the OEM versions because they are engineered for performance, not just price.
Best advice
The law makes independent workshops accountable, but accepting substitute parts from any unqualified supplier is seriously bad policy. Specifically, the Graeme Cooper team includes qualified experts who know exactly what best suits the circumstances.