What happens when you decline a delivery extension

[karolsb23]

I am working with a seller who already asked for the fifth time to extend the delivery time. I even wanted to accept it, despite being tired and the project was long overdue, but this time he put as a reason to extend the request a justification that is not true, so I want to refuse. My question is if I refuse to extend the date to deliver the work, will the seller be able to request an extension again? I ask this because it’s okay if he asks, I just want him to put the real reason in the request