They pay a "manufacturer" who turns out to be a trading company. Registered capital of £2,000, a rented office, and a 30% markup you never see. Alibaba doesn't tell you which is which. Chinese company records do — if you can read them.
They discover the compliance problem after the container lands. The product is fine. The paperwork isn't. A pallet of upholstered furniture without the right fire safety documentation is a pallet you legally cannot sell in the UK.
They pay a middleman who won't tell them who makes their product. Which is fine, until the middleman raises prices, goes quiet, or goes under — and you have no supply chain of your own, because you never owned it.