Determining whether or not a referral source is helping your ROI is easily done with referral source stages.
Referral stage is a great feature for seeing how your referral sources are helping you with your sales numbers. VIA uses four referral stages:
No Referrals > New Referrals > Historical Referrals > New & Historical Referrals
New Referrals = Referrals in the past 6 months
Historical Referrals = Referrals greater than 6 months ago
New & Historical Referrals = Referrals in the past 6 months and greater than 6 months ago