Referrals are much easier to win than any other form of lead. There is nothing better than a recommendation from a satisfied existing client. You can educate clients to provide referrals. The best time is when you have just won a sale, especially if the lead is through a referral. For example.
‘Our business is built on referrals and that is how we manage to keep our costs down. Once we have finished the project and you are happy then I will ask you for a testimonial and a couple of people you know who might also benefit from …….. I hope that’s OK with you….’
As long as they do not say no then you have their permission to ask them for a testimonial and referrals at the appropriate point. Remember to follow up though as they will be expecting it.