> They earn a few good reviews somehow at the beginning (paid? from mad people?)

This shouldn't be too hard. Have a few friends order a "product" you never ship or even pay a few people on Fivver to do the same. Costs $25 tops. Hell, you can ship them an empty envelope to put some tracking on it.

If I were the scamming type (and I'm not in the least) I think a decent scam would be create a really good quality private label product. Sell for six months at a very small profit margin. After the good reviews and best seller rankings pour in replace the inventory with shitty quality product at a huge profit margin. It would take a long time for the sales to stop. The initial sales inertia would take some time to slow down.

Maybe that wouldn't work, who knows.