In that case, you have to trust 0-conf. It's safe enough unless we're talking about large purchases where buyers are incentive to double-spend. I believe 0 conf is safe enough.
But would it be safe for a payment processor to rely on SPV?
For example. Bitcoin.com wallet does strange things: low fee tx appear and disappear suddenly in the balance screen. You have to be sure that your POS detects low fee txs and warns you
I am considering using bcash made by Purse.io, since it can run in SPV mode. I will check if I can query the tx fee in this mode. If the fee is below 1 sat/b ....
.... I will set a waiting screen for 1 confirmation.
Take in mind that a low fee tx could take days to confirm!
Hm. I guess it would then be better to send the same coins back and then show a message that they should try again and pay a higher fee.
I don't know... A full node running BU or XT will detect < 1 sat/B under double spend attemp. A SPV depends on the connected nodes. I'm going to try if Bitcoin.com wallets detects it.
