I escrow.

OgNasty escrows.

If you look at my trust or OgNasty's trust we have done this often.

I would charge 1% and 0.0005 for tx fees.

So. The cost for a 0.5 pc is.  0.5 + .005 + .0005 or .5055 total

I hold the 0.5 until the buyer gets the gear. The buyer has 1 day to test it.

I release the 0.5 to the seller.

Or if the gear is doa I hold the coin the buyer returns the gear. Once seller gets a return I refund the buyer.