I'd go along with the letting hotel book a tour option. If you are there already and don't need to take a plane to get there ( as is usually the case when taking that tour from BA or Rio) then why even hassle this sending cc to stranger?
On the other hand.. I just received a holiday card from Pedro (aka Peter) who also does private tours ( guide) he IS GREAT. I had been trying to find his info to give you when you first posted this thread.
You might ask his opinion too.. and by the way..we did not pay him in advance.
privatetours.com.br