People get rat pups and weaned rats mixed up all the time, not saying you do but stores do. I went into a local shop to get a rat pup for a friend and the rat they gave me was not a pup. They clearly didn't understand that rats have a stage between fuzzy and weaned. I about back handed the ignorant guy who was arguing with me, but instead I nearly got him fired for cursing me out. So wherever you're getting your rodents from is ripping you off most likely.
Rat pinkie = Weight (Grams): 5.00 - 12.99
Rat pups = Weight (Grams): 20.00 - 29.99
Weaned Rats = Weight (Grams): 30.00 - 44.99
Now mice:
Hoppers = Weight (Grams): 7.00 - 12.99
Adult mice = Weight (Grams): 18.00 - 24.99
Adult mice(extra large) = Weight (Grams): 25.00 - 45.00