Gerbils do not generally bite, and you do not want to buy an animal that does. Gerbils will, however, nibble your finger a little to see if you are edible. This is much different than a bite. If you put your hand into the cage a gerbil should be naturally curious and will come to give you a good sniff. Animals that do not get up or seem lethargic should be avoided.
Gerbils have different personalities than hamsters.
Plastic homes with lots of tunnels look fun, but they are not safe for gerbils. Gerbils, which are rodents, must chew constantly to wear their teeth down. All rodents teeth grow throughout their entire lives. Hard plastic, such as in tunnels and certain cages, may break off in shards that will damage your gerbils stomach and possibly kill it. These types of cages and tunnels are designed for hamsters.