How do I make sure I get the retainer fee?

[Ashley Moraru]

I have three clients that assure me they will pay a $150 Retainer fee once I find them a house for them to rent. They are all roommates that are desperate to move out asap for their lease ended weeks ago. They also do not have the credit. I read online that usually sellers pay this fee. I did contact listing online for them but as a new beginning in real estate.. how should I continue this process? Some will say it is not worth it, however learning the process could be beneficial.