I'll just play the devils advocate here and while agree there is no excuse for obvious flaws, having been in online and real world retail literally since I was born I'll just say that people can expect an awful lot from a mass produced item. When I was selling high end pocket knives I'd get guys wanting to return a knife because the blade was off centre by .02mm, yes it was a $500 pocket knife, yes it was also produced in a factory that had an expected quota of finished items for the staff to produce daily. I think that what happens is people see custom made very high end items online, gear that has taken a single craftsman weeks to produce, then expect the same level of fit and finish in a mass produced item. You get what you pay for for, if you want perfection be prepared to pay a luthier or custom shop prices. I have only bought 2 new guitars, a Korean Gretsch and a Japanese Fender neither is 100% perfect but for the prices I'm amazed at the quality. So yea, there will always be those Monday morning or Friday afternoon guitars that slip through QC with a fault but a realistic expectation of what you are going to get for your money goes a long way.
My biggest gripe with Ebay sellers is the old click bait/up-sell ploy. They advertise an amp or guitar for a good price, then after you buy it they message that their stock count was wrong and they don't actually have one, but can offer $20 off a higher priced item. Some will also say it might take a week to process your refund. Don't fall for it, demand the refund immediately or you'll report them to both Ebay and consumer affairs. I've had this done to me twice with big online stores and my nephew had it done to him by one of the same stores, so it's obviously their standard mode of operation.
edited to say I once had a guy send me a photo he had taken with a MICROSCOPE of the tip on a knife blade showing it had minuscule scratches and demanding a refund because it was "faulty".