I can't support this because of the damage this can do to legitimate businesses that have been around for years. There's many spiteful people who will enjoy nothing more than to put down another business using guest accounts/fake customers. Proof in these instances is vital to make a claim of their legitimacy when they're trying to tarnish someone's name.
I like
@Jason's suggestion on the previous page, I'm going to suggest this in addition to it:
Currently we don't allow any negative feedback or experiences (even
with proof) in someone's vouch thread, but only on their service thread which gets buried within a day or two after some bumps. My suggestion is we allow negative feedback/experiences, as long as they're backed up with proof within vouch threads. If a user has repeatedly delayed work, or been excessively rude/unpleasant, customers should have the ability to leave negative feedback (with proof) where it's easily accessible; their vouch thread and not their service thread.