Totally agree with @Silversitters about not allowing hosts to hide dealbreakers and spring them on sitters till the welcome guide and get away with it, for example.
I accepted a sit and then received the welcome guide and learned that one dog needed to be let out overnight to do his business and the other was prone to diarrhea. I immediately let the host know to cancel the sit, because I would’ve never accepted knowing that key info.
The host then said the info was outdated and that was no longer a problem, but I stayed on message: I wouldn’t do the sit.
From my POV, I prefer to stay matter of fact (including avoiding emotions like disappointment or anger, because that can turn people defensive or combative) when having such exchanges. I start low key at the outset, without mentioning that I’d contact THS or such. So for example, I simply messaged:
“Hi, XX. I just read the welcome guide. Thanks for sending. Unfortunately, I can’t sit if pets (need X or are prone to X), so would you please unconfirm me for sitting?”
When the host replied that X was no longer a problem, I just said: “Thanks. I don’t want to take the chance.”
At that point, the host canceled the sit.
Why I take this approach: If you raise the idea of contacting THS at the outset, that can unnecessarily trigger a host and turn the conversation threatening. Instead, I start neutral and low key and see if that works. If it does, then I’m good — I’ve quickly achieved my goal of getting the host to cancel.
If they don’t cancel in that case, I can always then say I’ll contact membership services. I’d still frame it neutrally tone wise if so. Like I’d say something like, “Unfortunately, I won’t be doing the sit. Would you please cancel it so we can save time and skip getting THS membership services involved?”
Why I’d frame it like so: When I say I won’t be doing the sit, I’m making it a nonnegotiable statement of fact. And I highlight that we can save time by not getting THS involved, because that’s also in the host’s interest, since they’re not going to be able to force me to show up for the sit.
For me, starting low key, staying polite and avoiding unnecessarily escalating awkward conversations tends to work quickly in various situations, well beyond sitting, like professionally. People tend to do what I ask without drama. If they don’t, I tend escalate only gradually, as little as possible, because I keep my goal in mind — I just want them to comply. I don’t want to unnecessarily trigger them and have them dig in their heels. That would just waste my time.
I have it in me to go scorched earth, but I rarely do something like that unless I judge it effective or necessary. That’s rarely necessary. It would usually be counter productive.