Commercial, rental, residential, multi family, vacant land. If it's real property, it can be put on the MLS. Sometimes with commercial or some multifamily properties, the owners do not wish the property to be "publically" know that it's for sale. I.e. no MLS, no sign, etc.
Usually, in these as well as all cases, the agent needs to use additional marketing techniques to try to get buyers via special magazines, networking with other real estate agents across the country, using specialized web sites which deal with investors.
There are numerous methods which some real estate agents can use to sell specialty properties, whether it be commercial or muti million dollar homes.
The expertise is out there.
Terrence Charest, e-Pro