[Acers]

well i have done many projects for people and mostly without upfront payment, Ofcourse that also means not doing every project that comes along. You can know what type the person by the way he posts or writes his requirements. And better still over a period of time the old regulars come to you or refer people so it works pretty well.
At the end of the day you have to show a bit of trust in him.
About people not listing requirements, sometimes(not always though) its also cos they don't want to divulge the project to everyone esp the rival board owners.