want to sell bluetooth speaker but the most likely buyer will be a non muslim. the speaker will most likely be used to listen to music or other haram aloud. The speaker is also quite expensive. is it permissible to sell it? do I take part in sin by selling it or am I not accountable for their sin?

Ustadh AbdulAziz al-Haqqan

Selling the speaker is allowed, as the scholars usually give a general answer like a device that can be used for both good and evil may be sold. But if you know this particular buyer is buying it for what is forbidden, do not sell it to him.