Hello @aivset ! Welcome to THS and the forum!
In my experience as a sitter with only a few sits booked far in advance, they did not cancel but the dates ended up being tweaked, they were either extended or shortened. We, as sitters, ended up having to cancel the sit that was shortened as the exorbitant price of air fare for a shortened stay was not feasible. The other sits went through and were fabulous.
This has been discussed in the past. Read the posts that precede yours in this topic and take a look at this one too:
https://forum.trustedhousesitters.com/t/list-now-or-closer-to-october-sitters-what-do-you-think/
And yes, you should tactfully post your restrictions in your listing, i.e., we request no guests. And you should certainly state the length of time the pet can be left alone. This is important information for sitters. Only sitters who can comply with those requirements will apply for your sit. And yes, it’s all based on trust but you have a sitter’s profile, reviews and application in front of you, and after that, you should arrange a phone or video call. All of these components will help you know if a sitter is a good fit.