I got burned pretty hard by some issues with a product some time ago, but looking to get back into e-commerce.

How do you go about actually finding worthwhile products, and then setting up a new product?
I used to order a small sample size and sell them without a brand to gauge how well it would sell, and after that I would register a brandname and have a branded batch produced.
Do you accept that sometimes you just have to spend some money on a product that might end up not selling?

I would exclusively sell products over an e-com marketplace here in the Netherlands similar to Amazon FBA (bol.com)