For people in the Netherlands and Belgium: Bol.com.

For elsewhere: AliExpress, Temu, Vinted (European).

For more specialised services:

Furniture: IKEA (Swedish)
Clothes: Zalando (German)
Food delivery: Jumia (German), HelloFresh (German).

Generally, it's best to buy directly from the companies themselves. Buy from small or mid-sized companies. You'll skip on the high prices that way, as there's no markup. Additionally, since you are not one of millions of consumers - but one of a few hundred, they will care more about you.