The camera sells, returns and sells again.
SKU R002 stays with the same camera. The first sale S002 receives $100. After $15 fees, $8 postage and $2 packaging, sale cash is $75.
Return RT001 pays a $100 refund and $6 return shipping, with $12 fees credited: a −$94 cash adjustment. Restocking restores the camera's $30 cost basis. First-sale contribution is −$19.
The later sale S003 receives $90. After $12 fees, $8 postage and $2 packaging, sale cash is $68. Subtracting its $30 basis gives $38 contribution. Across both sales: −$19 + $38 = $19.

