The short answer is that a recruiter will do whatever is necessary to get the right candidates into your open positions.
In many cases, a company's reputation precedes it - for better or for worse! The recruiter may have no trouble convincing candidates to interview for Company A, who is well-known international in its space as a strong best practices organisation with fair compensation rates. Company B may be equally well-known for its rigid policies and notoriously misguided sales tactics. In that case, a recruiter will have to sell the heck out of the position to get even an active jobseeker in for an interview.
The same is true for unknown startups. A recruiter will have to sell the position to potential candidates. "You've never heard of them," they might say, "but they raised $20MM in their last round of investment-seeking, from X, Y, and Z well-known VCs. John Doe, who was a partner in Super Successful Startup From Three Years Ago Inc, is on the board, and they're looking for a Director to help kick off a new project in a promising space that nobody's really explored before." Stuff like that. The recruiter will pitch an unknown company based on its assets and strengths.
This part of recruiting is similar to sales; it takes one individual talking to another to try and reel candidates in if the company's new or unknown (or it has a less-than-stellar reputation).
(This information comes from my experience as a researcher for a recruiting firm focusing on C-level and VP-level positions in HR, finance, legal, and marketing - to give some context.)