I have found rentomobile.com and Tany97.com to be very reliable. The cars from tany used to be a bit older but I never had any problems with them. Rentomobile cars were generaly newer. The prices from these are alot cheaper then the international chains. Tany have a desk at the airport, Rentomobile dont but I have never had an issue with meeting the rep at the airport
yes you can rent in bansko, There are a couple of places in the main street. The Kempinski looks nice, i have not stayed there but I went infor a look around. It is next to the gondola.