Data from field experiments in Southampton by Florian Foos shows what the impact of canvassing on voters is. more
The rather more mundane reality is that although overall the public is pretty polite to canvassers and willing to to answer questions, detailed policy issues only come up fairly infrequently. When they do, and if it is something you don’t know about, a polite request to take their contact details so that a colleague can reply in more detail works just fine.
In other words: if you’ve not been canvassing before, do give it a try with a local team – almost everyone comes away from their first canvassing experience saying it was easier and more straight-forward than they thought it would be. (And don’t worry, you don’t often encounter parrots.)