Generally quality costs money. Especially with CF, where it's not easy to tell once the product is finished. What counts is the care and attention to detail during manufacture, and the quality of the materials. You will only know whether the epoxy was properly cured when it breaks (or doesn't), and whether it was stored properly and so on. The design is also important, it's really easy to skimp on materials or get the layup wrong in key places, and if you don't destructively test a bunch of them you'll never know.
What you really hope is that you have bought an unbranded off-market handlebar made in the same factory as the real thing, and that yours is one of the ones where they used excess/leftover proper materials at the end of a run. If you're really lucky they did well on QC one day and you have an actual genuine, made-to-spec name brand handlebar, just without the branding because the order was for 100, they made 110, and all of them passed QC... so they quietly sold the extras on eBay.
If you're not lucky, of course, what you have is where someone bought the real thing, made a mould from it, bought some cheap "carbon fibre" and epoxy, taught themselves to lay it up so it looks like the real thing, and is selling them for not much more than the cost of materials. If you're extra unlucky someone saw the idea, made a mould that looks similar, lays it up so it looks about right where the customer can see it, and will have vanished by the time you discover that it's junk.