@Cp1 In the first instance where someone was contacting you to advertise a service, yes, flag the user since this is against Airbnb's Terms of Service.
In the second instance, since it was an Inquiry about other dates, I would answer the question and then decline. I believe there is a option to check that the guest was asking about other dates. This is not unusual. I had one the other day. I just told the guest when the dates she would like would be available with a polite note that I was declining because she wasn't really wanting the dates in the Inquiry. Sending a Pre-Approval just confuses the issue.
You can decline Inquiries without being penalized by Airbnb. This happens all the time for one reason or another. Declining too many Reservation Requests, on the other hand, could get you into trouble if you decline an excessive number.
Hope this clears things up. 🙂