Unless they are NOS parts, low price on anything you see probably means it's not genuine. Buy from reputable sources or directly from the OEM (some now have retail direct buy due to the counterfeiting problem).
I've seen Walbro, Bosch, Denso Siemens, Huco, Hitachi, MSD copies, cheap and total junk. Some copies are hard to detect, others pretty easy if you are familiar with what the original stuff looked like.
On Ebay, they don't tolerate fake goods and you can get returns on these and probably have the vendor shut down by reporting them. You'll often see terms "xx like" or "xx compatible" or they will use an OEM part number. Real stuff will usually use the word "genuine" in the description. Use caution if your parts are shipping from the east but your brand is from the west.
Some people will go as far as forging stamped trademarks on the parts and logos on the packaging.