Here’s an example of when most us would expect THS to have already kicked off a host and their dog, but apparently haven’t: HO Allowed to List Dog That's Bitten and Aggressive
This is why I suggest (when possible) not canceling and instead shortening, so the sitter can warn others. If a sitter has already started a sit, to me, it should be kept on the record to help others avoid the same problems, especially if it’s so bad that the sitter has to leave early.