Simple
There are and always will be con artists in the world offering unbelievable deals. It has always been buyer beware. never make a purchase without doing research from an trusted seller.
Sometimes a trusted source will accidentally fail, perhaps not through their fault, but through others in the chain, but we have to allow for that.
The scam kits on ebay, Amazon, Wish, Aliexpress are fairly obvious, they all look the same, with a stupid price. The images are nearly always of half the kit parts only.
Buy from your trusted sources or someones recommendation only. Most buys do not realise that Ali express sellers expect you to negotiate and communicate with them to ensure you both agree on what your getting. Us Westerners do not seem to understand that philosophy and just plonk down our hard earned cash and there in lies the opportunist.
Unless you really want to risk your money find out what your getting. ie the Dodgy kit, the kit thats been in the humid attic for 20 years, the "i think its all there, I'm not a modeler just sell it it for a friend" , etc etc etc.
Were intelligent folk ( we build complex , difficult and frustrating models ( hmm maybe were not!)) we should be able to spot a scam easily enough. We know the price of the "Well made EU/Chinese kits" . The price does not vary much over sites. When it does unless its a special from the supplier, its obvious that it is either, 2nd hand, or a "deal you want to miss" product.
Yes there are bargains to be had sometimes, but these are far and few between.
The scams are thick at present because the regular asian suppliers are down and obviously there are enough gullible buyers to partake of the scam.