I had a few similar experiences with guinea pigs.
Name her Firebird, 'cause she’s a TransHam!
True dat. We bought our last guinea pig from a store. Said it was female. The big ol’ dragging balls it developed a couple months later told us otherwise. A later vet visit confirmed this.
The whole “have trouble sexing rodents” is one of the reasons we have ONE hamster. She really wanted two. Between the “I don’t really trust these people to give me two of the same gender” and the possibility of finding a hamster feeding on the brains of another hamster…one hamster is enough.
They sell Zombie Hamsters?
Yes, I know. Band name!