Second Hand Steam Deck

I'm moving in with my girlfriend. We don't have room for my desktop computer, or I wouldn't want to take it with me because it actually takes up a lot of space, considering that I play so little. For example, I haven't gambled at all in the last year. But my fingers are itching to continue playing Baldur's Gate 3. That's why I'm toying with the idea of buying a Steam deck.

But precisely because I play so little, I want it to be a second-hand deck.

I've seen a few 512GB OLED versions for around €400. Is that a good price (for Germany)? What should I look out for?