A Grand Slam referral or Jeff Faile (accountant) would be a large multi-location residential construction contractor that is unhappy with his/her current CPA.  This would give Jeff a stream of regular inbound revenue and very likely a gate opener to other contractors.  Jeff has a long history in the residential building products channel and this would resonate well with prospective clients in this same channel.  Instead of "I know a good CPA you might want to talk to" it is "I know a GREAT CPA with extensive history in the building products channel that I highly recommend you talk to."   A Home Run referral for Jeff would be a single location, owner/operator in this same channel.   Still a steady stream of inbound revenue but smaller volume.   An On Base referral would be a person or couple just wanting to get their annual taxes done.