I do not think that buying referrals will be fruitful all the times. These bought referrals may or may not remain active for long time. If they become inactive then you loose your money.
Instead, I prefer to have exchange of referrals. Here your referrals will reciprocate your help to them and so it is purely give and take. In such situation, if one of the party becomes inactive, then both are loosers and atleast you are not going to loose cash.