Most quotes come with a number of free revisions included. How many varies by category and specialist.
Where to see the count
The number of free revisions shows up on the quote before you approve, regardless of category. Worth glancing at so you know what you're getting.
Categories without revisions
One exception: Album/EP reviews don't have a revision concept. The reviewer's job is to give you their honest take, not to keep editing it. If you want a different angle, you'd commission a separate review.
If you want changes beyond what's included
During the revision phase, the specialist can send a "Request Additional Payment" with a short note explaining what the extra fee covers. Typical extras run from a few credits up to about 20 (so $5 to $20 in credits).
From there it's up to you: approve and the work continues, or decline. If you decline, the specialist can either send a new proposal or close out the project at the last deliverable you'd already approved.