They do audits. Before political parties submit their election returns anyway, they are audited in advance, but if we're dealing with millions of dollars in receipts, finding the receipt from the Tim Hortons perhaps provides too much of a burden. However, giving that over if there is an investigation, allowing the commissioner to require the production of that material is still within the bill and provides a more balanced approach.
On October 17th, 2018. See this statement in context.