They send something out so there is a record of something being sent and received.
Smarter scammers will send a larger box that could fit the goods inside and then if you open it and take a pic of an empty box or a box of packing peanuts, they'll argue (if they bother) that you're the scammer, you took the item out and claimed it wasn't there - which is also a known scam from the buyer side of things!
They're absolutely bloody everywhere - I bought a spare part for an aquarium filter... after six weeks, what turned up was two pairs of fake Ray Bans and of course when i went to look at the website... there was no way of contacting anyone, there was no where to direct anyone to report them either and I'd used a debit card and my bank will not, not after that time frame.
All those products you see on fb, and now also vinted, etsy, etc that look AMAZING and incredibly cheap, for example, fantasy felted hats, OOAK soft toys, incredible coats etc - part of the same family of scams, selling things that don't actually exist, using stolen product images and then sending out rubbish or a horrible parody of what you thought you were buying so that you have received something and if you try to argue the toss... they claim you stole the item/subbed it or have just disappeared before you can get to them.
Always use a payment system that will fight for your money back if necessary.
Always check there is a way of contacting the person/company you're buying from (and not just a webform that turns out not to actually send!).
If its too good to be true - it is.