Reach out to the market organizer directly if you haven't heard back. Start with an email or a phone number if they list one.
Social media works too if that doesn't get a response. Most organizers give a rough time frame for when they'll reply, so check the original listing or your application confirmation for that before assuming the worst.
If the event date gets close and you still haven't heard anything, treat that as a warning sign. Radio silence right up until the event is a common pattern with scam listings, so it's worth double checking the organizer's legitimacy before you show up or pay any fees.