@Karen32 Be careful about offering "full refunds" since you are only in a position to refund the tariff you would have recieved, and not the booking fee paid to and charged by Airbnb. The phrasing you use when writing to your guest is very important.
So you can let the guest know that they are welcome to cancel via Airbnb, and the refund will be processed automatically. They will receive the refund as per your cancellation policy; less any Airbnb fees.
To avoid feeling unduly responsible in future, perhaps preface booking confirmations with statements such as " I am sending you a pre-approval, once you have read through all the information on my listing, if you still feel that you are happy to go ahead then you are welcome to accept the offer of accommodation and confirm a reservation. Please also ensure that you are comfortable with the conditions of the "xx" cancellation policy. Include a link to the policy terms if you wish to.
Apart from that I will clarify that you do not personally need to do anything to issue the refund, if they have formally cancelled. In this case, the applicable refund will be sent directly to the guest.
It is of course essential that they actually initiate the cancellation via "My Trips" on their site; telling you via email does not initiate or bring into effect a cancellation.
I hope this information is helpful to you.
Sincere regards, Christine.