Hi,
I'd also be asking myself why he would want to trade a breeding pair of yellowbellies for a baby normal burm - the dollar value of those two sides is not exactly the same?
I'm thinking if he sold two adult proven yellowbellies he could buy a whole clutch of baby burms.
If the snakes look nice and you could live with it being two normal males then I see no downside.
Otherwise get the pics of the belly and look for the amount and intensity of the flames on the sides of the animals.
dr del