@Susan990 There are no penalties like there are for cancelling, but to be sure you can have your listing suspended for declining requests:
From Airbnb: “Hosts who have very low rates could face penalties, including having their listings paused”.
And proof of that, from this forum (only one of many):
https://community.withairbnb.com/t5/Hosting/Excessive-decline-warning/m-p/1449756#M344342
Your search placement can also be affected.
If I’m declining for messing up my calendar or my rates, I’ll take full responsibility. But I take issue with the fact that Airbnb gives hosts no easy ‘out’ when receiving inappropriate requests or facing guests who don’t supply information requested before booking, and fail to respond in a timely manner when asked for it. I should be able decline, when appropriate, and not have to worry about a thing. Instead we’re left facing the clock, fussing about and sweating it out, putting up with endless reminders from Airbnb to respond 😡With the deteriorating quality of Airbnb guest, the opportunities to have to decline are becoming more frequent so again, I’ll save mine for when I really need to use them.