I'm not sure what you mean by the store quarantining them.
To quarantine is to keep your new axolotls seperate from from any you already have, in order to observe them. This is to try and prevent your new additions from bringing any disease to your healthy axolotls.
You need to keep any new additions by themselves in their own tank for at least 4 weeks, if you notice any illness in this time, you cannot add them to your existing axolotls until any sickness is well and truly resolved.
A search of this website will point you in the direction of any symptoms which may indicate illness.