Craigslist is a classified service. My guess is the seller has decided to see if he or she can rent the unit. So If they rent it sooner than getting an offer they will remove it from sale listing. If they get an acceptable offer then they will remove it from Craigslist.
They are not doing anything wrong.
Craigslist a realtor can list a property for lease or sale.
We are listing agents based on listing agreement and how we market home we market venue of ways, based on clients or agents we are attracting to that particular property