One of the most important roles as a realtor is to set expectations for rental clients with regards to

• Availability
• Budget
• Turn-around
• Space

Some of the biggest shocks to renters include:

• Having pets drastically reduces what's available.  Large pets narrows the selection even further
• Expecting a landlord to keep a rental vacant for over a month greatly reduces your chance of getting the unit
• Short term leases (less than a year) cost a landlord substantially, both due to lost income from vacancy and the cost of restoring and finding a new renter
• If you've looked at a half a dozen units and everything is way off the mark, then things are very unlikely to improve.

As a realtor it's important to convey this information.  As a renter its important that your realize that ignoring your realtor's advice will quickly land you without a realtor.  No one likes to be ignored, but more importantly your realtor doesn't want to waste your time and the realtor's time chasing possibilities that will never happen.