S: (n) commission (a fee for services rendered based on a percentage of an amount received or collected or agreed to be paid (as distinguished from a salary)) "he works on commission"
S: (n) contingency fee (a fee that is payable only if the outcome is successful (as for an attorney's services))
S: (n) finder's fee (a fee that is paid to someone who finds a source of financial backing or to someone who brings people together for business purposes) "the agency got a finder's fee when their candidate was hired as the new CEO"
S: (n) licensing fee, license fee, license tax (a fee paid to the government for the privilege of being licensed to do something (as selling liquor or practicing medicine))