Bigger isn't always better
When selecting a recruiting service, don't just go with the biggest firm. Smaller firms may have a more focused pool of candidates, in terms of geography and industry, which means you won't have to sift through a stack of leads that cover too broad a spectrum.

Is there a volume discount?
Some online services set their price according to the number of qualified candidates they will recommend to you, 10 candidates for about $3,500, for example. If you need multiple searches, however, some might offer you volume discounts.

What if it doesn't work out?
Ask about the agency's policy if the person you hire ends up being a bad match for the company. Do they offer a replacement or a partial refund? This should be a primary concern because there's always a chance that the candidate might not work out.