We've all done it. Looked on eBay for car parts. And we've all seen the $100 full exhaust in polished stainless steel that looks 99% the same as the $1200 exhaust offered by the big brand name company. How do they do it?
It starts with one person trying to make a buck. Even a simple internet search will yield many overseas "manufacturers" that specialize in reverse engineering. Their communication skills are second to none, so even if you don't know Polynesian Nuk-Nuk, the language of whistles and pops, their agent "Brian" speaks better English than most of us.
Next, they purchase a brand name exhaust and send it overseas. Once the exhaust is in their hands, it goes to a real master craftsman who makes a prototype for the customer to review. It's flawless. The customer then orders 100 units to save on the enormous shipping costs. Once paid for and received though, it becomes apparent that the $2/hour crew did the work. Ever seen a Version 2 exhaust? This means changes were made for batch 2 due to poor craftsmanship, but Version 2 is better marketing than "Oops, the 14 year old screwed this one up, so here's take 2". Then they are sold on eBay and various sites through their distributor network. You better own a Persuasion Hammer and a sacrificial drill bit to waller out some bolt holes.
So it sounds like one person is sticking it to the big name companies right? Well, in the spirit of free enterprise, that same company will add "your" exhaust to their product catalog. Now "your" exhaust that you so proudly knocked off, is for sale to anyone who has the money. The cycle of fail is now complete.