You will never achieve a 100% success rate in recruiting successful volunteers, despite everyone's best intentions. However, you can increase the likelihood of your success by carefully considering and assessing your candidates before you ask them to serve.
When seeking volunteers to help you solicit gifts to your campaign, look for individuals who have as many of the following characteristics as possible:
Direct Experience: They have done this before, working on other campaigns, so they know how to solicit, have proven they can do it successfully, and will accept the assignment confident in the knowledge of what it calls for.
Related Experience: They have done annual fund solicitations or other, less challenging fundraising, in which they have demonstrated their ability to solicit successfully.
Relevant Experience: They have professional experience in a role that calls for the same kind of activity and accomplishment - focusing on a prospect, getting an appointment, making a proposal, and closing a sale.
Outgoing Personality: They are active in the community, are known to many people, are good communicators, and are well-regarded generally.
Commitment: They have demonstrated a real commitment, not only to your institution, but to the project(s) for which the campaign has been organized.
Direct Knowledge: They are familiar with your institution and its mission, history, programs, and constituency.
Philanthropic: They contribute to worthy causes (including, most especially, your institution) and understand the field. Also, they are prepared to make a campaign gift themselves, in the range in which they will be asking others to give.