Defer the referral email until some time has passed. Also include some incentive to refer somebody.
This was my reply to the referral email:
I could refer, but I have no incentives to... and haven’t really tried the app yet, so no. Come back with a value proposition and I might want to.
And this email should come at least a few days later, not now.
6 months free, extra scans, etc you name it.