Is it normal for a robo dwarf hamster to bite?

hey everyone i got robo dwarfs about 2 weeks ago one of my robos will let me touch them and pet them for like 3 min then it will bite me i take that as a hint that im done but the other one is sooooo scared i try to offer it food but it runs what should i do and is it normal for it to bite they said they dont bite at the pet store hmmmm. PS i jerk my hand away cause i get scared should i just keep my hand there plzzzzzzz answer thanks!