You've prompted me to add a link to blockchain on my mobile. I should have done that ages ago.
The main reason for my running a full node is to explore the variety of payment conditions that can be associated with a payment. One that interested me was a form of escrow where one could use a trusted party as a third signature for a 2 out of 3 release. Another is a time lock with possible reclaim to prove the availability of funds.
Unfortunately I haven't had the chance to research these, but hopefully I will be able to do so in the near future.
I've found this thread because Raspberry Pi was mentioned in
(and I'm about to build a Raspberry Pi node, and I'm searching for information)
I read thru the thread and I think I understand your problem.
If I'm right, you receive smaller payments for domain names in bitcoin, and you want to protect yourself from being scammed and lose the domain and the bitcoin payment too. You have to use free wifi sometimes, this makes the whole thing even more risky. Also you usually do this meeting the buyer personally somewhere.
As I'm about to install a small Lightning network node on the Raspberry Pi (and this is why I'm searching on the forum for information) the LN came into my mind as a possible solution for you. You don't need a Raspberry for this, just an LN wallet on a laptop.
I think you contact the buyer before the personal meeting via email, so you can tell the buyer to set up an LN wallet and send the funds to his LN wallet (like ZAP
https://zap.jackmallers.com or similar, I've found ZAP as the first one in the google search). This is not risky for the buyer because he can use his own LN wallet, if something goes wrong then he can easily send it back to his original address. You can also have your LN wallet to collect these payments at personal meetings.
So when you meet, all the buyer has to do is sending the payment via LN. It confirms instantly so you don't need to wait for a few confirmations (20-30 minutes). This also shortens the time available for hackers put their equipment together to mislead you about the payment (and this can be the key in your case).
After you can check the LN transaction on your laptop LN wallet (over the public WIFI), and also that time you can check the LN transaction on your smartphone, on a LN blockchain explorer, and if the two devices show that the transaction was done without a problem, you can hand over the domain name to the buyer.
If the buyer comes with a loaded LN wallet, this whole thing won't last as lons as you can drink a coffee or cappuccino.
I know that this is under testing now and we need to wait for some time to get it working without bugs and hassle, but I would think about it if I were you. If you sell those domains for years now over public WIFI, I would consider not to invest in tinkering boxes (just if you really interested in), because in a few months time you can have a chance to do the payment via the LN. Maybe those few months would be needed for your to set up your new equipment with the VPN, HTTPS, SSH and so on, to test it hard to be reliable, but if you can use LN, this all will not be necessary. (this is only my opinion, but others will surely correct me if I'm wrong).
Also, later on, you can set up a small website where you can accept LN payments for your domains, you can do that also when you meet the buyer personally (access the website from the buyer's laptop or mobile and sendig the payment also from there). In that case, when the buyer needs to initiate the payment over the public WIFI, the security will be his problem, not yours. In order to check if the payment was really successfull, you will have an easier situation, because of the really short confirmation of the LN transaction, hackers won't have the time to scam you.
Please let me know your thoughts, I was just wondering if LN can help you.