I'm pretty sure if a retailer sells a widget for $100 then the revenue is $100. COGS is $50. GMV is probably a term more useful in situations where the entity

I'm pretty sure if a retailer sells a widget for $100 then the revenue is $100. COGS is $50. GMV is probably a term more useful in situations where the entity is not a retailer per se, like eBay, who still wants a number to represent the value of the goods they are facilitating transactions upon. They don't own the items on auction so the purchase price is not revenue to them, but the fees are revenue.