I’m sorry, I don’t think it’s a great idea. You are admitting fault about being harsh, even though the guest didn’t say you were harsh (we did but we’re a tough audience). Don’t create a problem that you don’t already have. Along that same line, don’t admit to Airbnb that you were harsh to a guest, because anything in a message is telling Airbnb the same thing. I don’t have any expectation that this will escalate, but if it did, it would be better if you hadn’t said that. And don’t give the guest any ideas. Perhaps he did not think you were harsh. Always cover your own burro.
Also, there is no point in trying to make your stuff (mortgage, retirement, income, etc) your guest’s issue. It is not and it never comes across well. It doesn’t sound apologetic, it sounds defensive. Giving a bunch of excuses as to why you have an extra guest policy does not support your policy. If it is a reasonable, fair or just policy (and it is!) then you don’t need to justify it by explaining your personal circumstances.
We aren’t currently charging an extra guest fee, for various reasons but not because I don’t think it’s a great way to operate, because I do. We did charge an extra fee for every guest over the first one, both in our 2 person studio and also in our 4-5 person 2 bedroom apartments for nearly 3 years. I have been in the position to explain (because it doesn’t require justification) it quite a few times. I am going to show you what I say. I am not saying that there’s anything special about it or tooting my own horn, but only that it has been successful. I have never lost a booking because of our extra guest fee. The most common time, and I’m sure you know, is when people book for 1 person and then say, “we can’t wait” or something. Anyway, not sure if you’ll like it but it works for me:
I’m noticing now that you’ve booked for 1 Guest but it sounds like your Mom is coming too and will need to be added for insurance and Airbnb terms. Note that the price will change a bit ($20/ night), sorry that’s just the way it’s set-up (it’s a way to give solo travelers a discount).
I can send you a change request, adding your mom to the reservation, and you can either accept or decline once you see the new price. If it doesn’t fit into your plans, I understand either way (though we’d love to have you stay!).
In the case that I’m dealing with someone later in the game like you are, I would say something like:
The apartment is priced for one person with each additional person charged as an extra guest. It is set up this way so as to provide solo travelers, couples and small groups each with a fair price and to accommodate a larger portion of the Airbnb community.
You can see the spin. Now it’s not your personal circumstance that is the reason that the guest has to pay more for a second person. Now the guest has to pay more for a second person because you are a generous host that looks out for the whole Airbnb community and you are also now a host that gives discounts, as opposed to just a host that charges some people extra. Spin is not always a bad thing, sometimes it makes people feel better. It works. And, for us personally, it is the real reason that we charged per guest because I am an avid solo traveler.