What would you do? I need honest answers here

Since I joined this forum I've sold several extra parts to other members and I've always done so with a happy outcome for us both in mind. If seller made an honest mistake, and shipped UPS instead of USPS he should just say so and try to work it out. Of course if deliberate then he should refund to seller whether he wants to or not. Sadly, his silence speaks more directly to his unreasonableness than anything else in my book. I expect scams and unreasonableness from Ebay but not from within this small like minded community.