There are many ways that people are considered professional. If someone is paid to take your photo the photographer could be considered a professional. Usually the location wants their share; either to maintain the location, inconvience of other patrons, etc. Paperwork usually has to be done for insurance/liability issues. People like to sue
Best thing to do is call the place and ask them nicely and follow all rules. Go as far as asking them rules that signs or that they haven't covered; as people are not mind readers. Be courteous to other patrons.
I work at a location in which cosplayers have visited to take pictures and there's usually no problems. Photographers don't bring a ton of equipment that blocks the paths and we don't have complaints about them. Usually only a couple of people so it's no big deal. Sometimes we have to yell at people for climbing things, but it's not to often.