In general, you have a contract in place first. Sometimes they'll send in nameless resumes, and if the hiring manager likes them, they get the contract in place then. I've had clueless recruiters do that to me, and I suspect some are fake resumes. I've gotten good at spotting recruiter submissions and just ignore them now.
My clients have me do all the coordination with the candidate, and we keep each other in the loop. I only work with reputable companies, but there are a couple lawyers out there who specialize in collecting from deadbeat staffing clients, so it is a risk. I understand it's more an issue with small businesses (kind of like software consulting).
The contract will stipulate grace periods, and usually if the candidate applied in the last 6 months, through any means, you are ineligible for the placement fee.
The first recruiter to submit the candidate "wins," and of course this includes internal recruiters, who get credit for website applications. I was bitten my this once, where I essentially placed a client by selling them on someone who was already in their system, but had been ignored. He had shotgunned his resume and didn't pay attention where, so he wasn't lying when he said he wasn't familiar with the company. It was painful to lose out, but at least he and the hiring manager are very happy with me, so small consolation.
This "first submission wins" has motivated recruiters to submit resumes as soon as they get them, before even talking to the applicant. To me, that is unethical and would hurt my reputation. However, I've had job seekers tell me they trust me to apply to relevant jobs on their behalf. Obviously, that's very different.
