I'm really sorry to read your story and hope it does not happen to us.
If your listing is "entire place", guest may be entitled to a certain amount of privacy preventing hosts from arriving on the property without notice except for emergencies.
If the listing is a "shared place" guest are not entitled to 100% privacy in all areas of the property.
Did you notify the guests in advance that you would be arriving on the property?
Does your listing state you meet guests at check-in or do you promote a "self check-in" process?
If self check-in, guests do not expect to meet the host at check-in and doing so could invade their expected privacy.
As hosts, we have to be extra extra careful to ensure that the guest expectations regarding privacy are not only met, but exceeded.
Once again, I'm sorry this happened.