Only good experiences (amazon.de), friendly, good service. Year for year voted to be amongst the safest sites in Germany, concerning banking transactions.
On the other hand: internet business kills local stores. I used amazon a lot, but have moved away from that again, and now order there only when I can't get the item in town, or only for >significantly< more money. It's many of >our< jobs we kill when making some big fishes even bigger, and giving up on the local diversity of small shops.
Support small trade! They want to live, too.
See, that easily a question for banking safety can turn into a political declaration!