Is it normal for a broker to request a deposit prior to conducting a due diligence?

Hello. I was wondering if this is simply standard practice of business brokers as I've never used one before. The brokerage firm that brokered a deal between a seller & myself is requesting them I send them a certified check for $5000 prior to conducting my due diligence. The broker said it's simply a good faith deposit that will be refunded once I complete the due diligence whether I commit to the purchase or not. However, I found it odd given it's a non-binding agreement so I thought the deposit had no bearing since I not committing to anything. I mean what would be the reason they keep it other than if I not show up? Do all brokers do this or just a select few? Thank you for any feedback that you can provide.