Customers who engage free photographers with no other benefit to the photographer may have no legal right to demand anything since their demands are not likely to be enforced by a court of law.
As nightmare has said, that does not stop their mouth from posting all over the shop to complain; jsut as anyone can complain about anything, regardless of amount paid, who the person is, etc etc. There are also people in the wrong who complain, so if its just complaints alone, nothing can stop them (short of killing them).
Also, if a customer who got free services tried to complain in a forum of sorts, there is a good chance that they will not be taken seriously by the audience reading the complaint; and I've seen replies in ST Forum's online discussion board who essentially lamblasts complainants of free services. Of course, if they are thick skinned enough, anyone can complain about anything.
Hey, one queries... how about these 2 situations below? Whether the client has any legal rights to sue?
Photographer did not charge but client pay him an allowance, sort of to cover transport and effort?
Client gives an ang pow for his effort