@Susan990 Airbnb has never required any sort of documentation for either service dogs or ESA's, so a guest has always been able to just claim their pet is an assistance animal and walk right in. With the recent update to the policy though, a host may now refuse an ESA, or can charge a pet fee. Hosts are still required to accept a service dog though (or miniature horse!!), except under certain limited circumstances, and can't ask for a fee. No document required.
https://www.airbnb.ca/help/article/1869/accessibility-policy
Note that there are requirements that the guest who claims assistance animal must adhere to with their animal. Which helps weed out the fraudsters.