You are combining like three different threads. I paid 3 BTC and looking for a refund of 3 BTCs. He made an offer on my device and I told him what I thought about his offer. I never said refund me what I think the device is worth. Please read and understand what I write, not that hard.
Seems I did, sorry.
But I stand for the first point (about the refund). If the 3 BTC that you send them were worth X euros when you send them, you paid X euros, and you are entitled to a refund of X euros.