There is a feature in bitcoin called replace-by-fee (https://en.bitcoin.it/wiki/Replace_by_fee). But that is not completely analogous to a refund because vendors will wait many blocks before accepting a transaction (to prevent finney attack).

If you want to have a third party mediate the exchange, you can use a multi-signature transaction (https://monerodocs.org/multisignature/). For example you send the cryptocurrency to a 2-of-3 address where the mediator, the vendor, and the customer each hold a key and two of them are needed to move the funds (the mediator sides with either vendor or customer, or the vendor and customer both side against the mediator). Or you can send the cryptocurrency to a 2-of-2 address, which allows the customer to permanently withhold the funds from the vendor at the cost of withholding some funds from themself that they put down ahead of time, like an escrow that is locked in case of dispute.

One way to get something like chargeback is 2-of-3 multisig. The transaction has to be signed by any two of: sender, receiver, and a neutral arbitrator. If sender and receiver agree, the arbitrator never has to hear about the transaction.

That is nothing like chargeback. It would be like chargeback if you could rescind a signature, once you notice a mistake.

That wouldn't be chargeback either. You have to get the bank to do the chargeback, you can't just do it yourself.

If you wanted something more like that, you could pay via a smart contract that holds the funds in escrow for a while, with the arbitrator key able to refund the money to you.

You cannot, which is what grandparent was complaining about.

You can, with script. Most of us don't want that particular "feature".