@Carolyn288 There really isn't a universal guide for the amount of a Security Deposit since each listing is unique and contains various levels of valuable furnishings, appliances, etc.
In my entire home listing (2 bedrooms, 2 baths) I have removed any items that a) are irreplaceable and or b) would be emotionally devastating to lose. And, I don't have many very expensive items that could be damaged.
With those caveats, I placed a $250 Security Deposit for major damages taking into consideration that there will be normal wear and tear over time that I would not hold against the guest.
In three years I've only made 2 claims against the Security Deposit. One was for stained pillow cases caused by dyes associated with a sleeping mask (I have no idea how that happened) and the other was for a lost key which required that locks be changed. Both claims were for less than $100.
Since Security Deposits are not charged to guests unless a claim is made and is either agreed to by the guest or, in the case of mediation, Airbnb, you can set any amount you want. Take a look around your listing and see what the worst case senario might be and then evaluate the likelyhood it would occur. Also, if you have a non-smoking listing, you might investigate how much it would cost to remove the smoke smell in the event a guest violated that rule. Most hotels, I believe, have a standard policy of charging $200 for smoking in a non-smoking room.
I hope this is helpful!
Clare
