I agree with B0B in that only a version of #1 would make sense, #2 and #3 are too centralized or complicated for verification (Twitter’s get hacked).
I’m not too fond of “partial payment” from a buyers perspective, would likely cause confusion or manual mistakes in my opinion.
Though I think some sort of restriction is very needed for the ability to close the dispenser when an unconfirmed dispense is waiting to confirm.
Some sort of “auto lock” on the ability to close the dispenser when an unconfirmed tx is seen could work.
Though, many people have brought up the idea a “troll” user could send very low fee tx’s to “block” the closing of the dispenser for a prolonged period.
There would have to be a high incentive to get the tx confirmed within “X” amount of blocks (and quicker than low spam tx’s if there are some in unconfirmed), which would fall on the buyers responsibility. You would have to put a disclaimer that said “if your tx does not confirm in X blocks” you MAY not receive your token and explain why or how. You are recommended to use ULTRA high fee setting (or something like that).
People brought up an idea of “first in queue” but this idea allows for the “trolls.” But with an auto-lock function on close dispenser enabled it would still be “highest tx fee of buyer first.”
This could end the need for “trusted” dispenser owners assuming the buyer confirmed in X blocks easily. Yet it would still cause buyer induced mayhem if a heavily sought after token got “bought out” and some users paid high fee’s and received the token even though their tx was “later.” But when the dispenser ran out of tokens to dispense, some unconfirmed tx’s at “previous reasonable prices” would be front run.
Again though, this could be at the users risk if they are trying to “beat” low fee tx’s that are unconfirmed. Which I think has been fended off somewhat xchain showing unconfirmed tx’s as “tokens already being dispensed.”
It could solve at least a part of the problem and reduce scammers.
Still pondering some sort of idea to solve this from someone who knows much less about the coding side. ¯_(ツ)_/¯
Edit: I’m glad I pondered this but the ultimate flaw is still that the “scammer” could just “buy back” the token with a huge fee with unconfirmed tx’s still in queue. So it might not work. 