I have an incoming transaction from someone that will gonna purchased my item. The problem is the transaction is already stuck in an unconfirmed state for so many days due to the very low transaction fee set by my buyer. He doesn't want to bump the fee and we are just both waiting to confirm for whatever time it is. I'm planning to cancel the deal but the problem is the transaction is still not failed or confirmed.
I wonder if there is a method to cancel this kind of transaction manually because I'm not interested anymore in the deal even if it needed to be paid by me just stop this madness of badgering.
The solution to your situation depends on the type of wallet you used to sign the transaction. If your wallet has RBF (Replace-By-Fee) enabled by default (you can check this by scanning the transaction ID on the Blockchair explorer or your wallet settings), you can increase the transaction fee by replacing the transaction with a higher sats to expedite its confirmation. However, if your wallet doesn't have RBF enabled or you didn't enable it prior to the initiation, there is no way to fasten your transaction, maybe accelerators can help but then, depends on the quantity of your input(s).
Alternatively, you can consider performing a Child Pays for Parent (CPFP) transaction. To provide a clearer explanation, it would be helpful if you shared the transaction ID since it involves a transaction between two individuals. If you are anticipating any change in that transaction, you can initiate a CPFP transaction, which should facilitate a quicker confirmation or, you could also advise the recipient to initiate the CPFP transaction and you guys can settle about that later.