Very good topic Nil,
Since it's a service exchange in contractual terms, deciding the contribution is left to the parties agreeing for the same. Most of the private consultancies who do not have much backup companies with them do this, and in fact, many collect the fixed salary amount even before the candidate joins and gets his salary. As I have observed, many of the candidates placed by them will be chosen as probationers or trainers, and a few are from an entry-level background, and their employment is not guaranteed. There are genuine consultancies as well, but I suggest the candidates believe in and rely upon those consultancies which have company backups or agreements with the companies for placements. Most of such consultancies hardly collect any fees from candidates as they will be getting their pay from the companies that hired them for sourcing candidates.