As a buyer, it’s in your interest.
Let’s say you want a web page designed. You order it. The seller delivers a wonderful site, but there’s one problem. There’s no custom video, because the seller is a web designer, not a videographer.
So you file a modification request. The seller asks why you didn’t tell him you needed a video before you ordered, and you say you would have but you need it right away.
The seller can’t modify the project because its not in his skill set. Cancel the order now, after the seller worked hard and delivered a wonderful project? That’s not fair to the seller, because he won’t get paid for his hard work.
It’s not fair to you, either, because you’ll either get stuck in modification hell, or you’ll end up paying for a project you can’t use.
And mentioning the need for a custom video in the requirements section when you order (you do fill out the requirements in detail, right?) doesn’t help either, because once you complete the requirements the order goes through, regardless of whatever you put in it.
It happens all the time. Voiceover artists are asked to compose music, musicians to create music videos, and virtual assistants get orders to file legal briefs. Nobody is happy when this happens.
Many, if not most sellers respond to orders within an hour. That’s not a long time to wait for a gig to start.
As I said, it’s in the buyer’s interest too.