Third party fundraisers, especially if run by volunteers, can be a very effective and efficient way to fundraise.  However, charities are not allowed to just outsource receipting functions.  Here is a document from CRA on third party fundraisers and receipting

Policy Commentary
Release Date
February 26, 2003
Reference Number
CPC – 026
Subject
Fundraising – Third-party fundraisers for the benefit of a particular registered charity
Purpose
To clarify the Directorate’s policy regarding fundraising events for the benefit of a particular registered charity.
Definitions
amount of advantage:  the total value of all property, services, compensation or other benefits to which the donor of a property, or a person not dealing at arm’s length with the donor, is entitled as partial consideration for, or in gratitude for, the gift
intention to give:  the amount of the advantage that accrues to the donor does not exceed 80% of the fair market value of the property transferred
eligible amount of gift:  the amount by which the fair market value of the property that is the subject of the gift exceeds the amount of the advantage, if any, in respect of a gift

Commentary

1. Under the Income Tax Act, registered charities can issue official donation receipts to donors for gifts. This tax-receipting privilege is not to be casually farmed out to third parties, even if some of the resulting funds will be flowing back to the charity. A charity that substantially relinquishes to a third party its receipt-issuing function or the control over the funds that are donated to it, can jeopardize its registered status.

2. A registered charity can enroll a third-party organization or retain a fundraiser or other contractor as an agent to organize a fundraising event. However, the charity should maintain control over all monies that are earned as part of the event, and over the receipts that are issued for part of those monies.

3. If the charity does not run the event substantially by itself, through its own employees or volunteers, it should:
a. put in place a written agreement setting out the modalities of the fundraising arrangement;
b. ensure that official donation receipts are only issued to donors for the eligible amount of the gift;
c. ensure that official donation receipts are signed by an authorized individual in conformity with ss. 3501(1)(i), 3501(2), 3501(3) and 3502 of the Income Tax Regulations;
d. be able to provide to the Canada Revenue Agency a full accounting of the monies or that portion of the monies donated to it, and the receipts that were issued in return;
e. be able to account to the Canada Revenue Agency for the amount of the advantage received by the participants as a result of their participation in the fundraising event.

References
• Income Tax Technical News, Issue 26.
• Registered Charities: Operating Outside Canada, RC4106.
• Income Tax Act, R.S.C. 1985 (5th supp.) c. 1, ss. 248(30), (31) and (32).
• Income Tax Regulations, C.R.C. 1978, c. 945, s. 3501(1).