commission depends; if you are paying already enough rent the agents cover it from landlord side

otherwise 15day rent for them is enough,.

the best way is to set your priorities/budget, area and alternate choices and then roam around looking for banners "For Rent" , plus check daily ads in news papers, online ads, ask for references in your family/friends .. i believe over 60% accomodation are not properly advertised and just street search, word of mouth and building caretakers support normally get you a nice apartment of your choice

my 2 cents

good luck