@SoraFan23 are you at a good place in your game?
I only ask this because, in all seriousness, I am a very fickle person and my trades are generally fast, so yes, I understand your frustration. If I'm forced to wait around, then yeah it rubs me the wrong way...but...as the seller, you are in complete control.
If you're in a good place in your game, and don't need the business, just shut down the slow trades. If someone's taking too long, just shoot them a message saying you're moving on and thank them for their interest. I do. This way you don't have to worry about feedback repercussions.