Genuine parts can be quite expensive depending of the type of vehicle you have, BMW, Audi etc, however buying pattern parts to save a few pounds is, in my opinion, false economy and you never know quite what you get.
When the manufacturer first produces the panel the presses are brand new and turn out perfect parts, however after say every 10,000 units the presses become deformed, holes slightly out of line and the panels mis-shaped.
The manufacturers may run these presses for up to 50,000 units before the press quality is no longer acceptable, they then change the press in order to maintain the quality but what happens to the old press?
Usually the old presses are sold on to a third party who then re-produces a panel using the original pattern, hence a pattern part, a lot cheaper but nowhere near the quality of the original part.
The most common problem with pattern parts is the repair garage, more often than not ( I am ashamed to say ) the customer will be charged full retail for a genuine part but a pattern part fitted, this gives the garage a high profit margin but the customer simply doesn’t get what they pay for.