It is common for Internet brokers to pass around contracts and fee agreements that in their typical format bring exposure to their enforceability. First of all it is important to understand is that intelligent/experiened signatories will not sign their name to incomplete documents because it the equivalent of asking for trouble and abuse.
It is common for brokers expect a principal and/or payer to sign an incomplete document and then send it back out into the Internet for anybody to fill their name and credentials into which means the signatory has no idea of what exactly he/she was signing their name to at the time of signing. From a legal enforceability standpoint it begs to be challenged as enforceable.
These polluted documents are circulated among the brokers who stretch the document all around as well as make changes to the wording and formatting of the document. It is largely an insane process yet these insane processes are practiced by thousands of broker/internmediaries that actually think there is sanity to these processes from a legal standpoint.
A signatory has no obligation to pay anyone not listed on a document at the time of signing. So it stands to reason that it is clueless to think that a signatory is obligated to pay parties that show-up later in the processes of common Internet intermediaries.