You’ll get a buyer that doesn’t value you, your time or your work. They won’t even know what they want, they’ll just keep changing their order.
Even if you deliver a product they want which is hard to do with how vaguely they communicate, they will ask for extras not mentioned at the beginning that you can’t give them then they’ll demand you lower the already insanely low price to half.
Following this, they won’t understand that you can’t just change the price mid order so you’ll contact customer support for help. They’ll tell you to 1) explain yourself to the buyer to force the sale and accept a most likely negative review or 2) cancel the order and make a new one for half the price.
You’ll take the second option after spending way too long on the gig because at least then you can earn $5 and because you’re a new seller it’s the best option to avoid losing all future opportunities on Fiverr.
The buyer won’t get it and be confused or at least feign confusion, most likely they’ve just stolen your work. After all this you get the pleasure of sitting around waiting for customer service to cancel the order and lower your completion rate and ranking. I mean hypothetically, it probably won’t happen to anyone.
On an unrelated note here’s 3 pieces of orphaned music that anyone can have for free to use for whatever purpose they like: https://www.dropbox.com/sh/jppaw5mppyqu41v/AAAnSf1lLrRoRWCHO3xqt9xIa?dl=0