Well the problem for most to find them is the language, 'cause there are plenty of them, but not in ‘English only’ written.
[https://www.2dehands.be/] (https://www.2dehands.be/) for example, in the old days http://www…marktplaats.nl/ use to be mostly secondhand, to my idea. Both in Dutch, 2dehands also with French written ads.
Then you can have a look at ‘kleinanzeigen’ in German, meaning indeed ‘small ads’: for example https://m.ebay-kleinanzeigen.de/ or for example https://www.kleinanzeigen.de/ and at https://www.kleinanzeigen.at/ in Austria.
So look up the words “ads, music, bass” in the other languages, if you use google mostly you get the biggest platforms for those languages / countries on the first page. (Well almost… , read on…)
But, and that is a BIG but: search results also change depending on your settings which language to use in your search results. Something to consider changing searching in different languages, to change your browser and google (or other searchengine settings)
Let me give a small example: ‘ads’ translated to Danish is mostly translated as ‘annoncer’ by google or deepl.com: yet that’s not the translation you need as an advertisement (singular) is translated as ‘reklame’ in Danish.
So when searching with ‘annoncer’ (when you think you’re searching in Danish) with google you end up with the results of the French ‘annoncer’ which in English means ‘announce’ … after changing your google settings to show Danish language results first you get to see more results that are in line with ‘reklame’.
Now, if you know the differences in languages and enjoy using them, all is open for you to find. Let me just finish saying it in yet another language: “Gelok mei sykjen”
See if you can spot what language from Europe that is